[Android General] pndwal:
Not a dev, but -

I'd check what system/build.prop values have changed from stock.

It's easy to edit these back using a buildprop editor from playstore. Reboot, see if problems are solved and check that buildprop entries have stuck. If it works, save modified build.prop file (using file manager with root explorer permissions), extract ROM, replace build.prop (check file permission properties are still "rw- r-- r--") and recompress.

Check telephony related anomalies especially. Stock TB3-850F values:

ro.lenovo.tablet=wifi

ro.lenovo.sim=none

persist.sys.lenovo.ltetype=NONE

persist.radio.default.sim=0

persist.radio.mobile.data=0,0

ril.telephony.mode=0

Here is complete build.prop from stock TB3-850F:

# begin build properties
# autogenerated by buildinfo.sh
ro.build.id=MRA58K
ro.build.display.id=TB3-850F_S100031_171010_ROW
ro.build.version.incremental=TB3-850F_S100031_171010_ROW
ro.build.version.sdk=23
ro.build.version.preview_sdk=0
ro.build.version.codename=REL
ro.build.version.all_codenames=REL
ro.build.version.release=6.0
ro.build.version.security_patch=2017-09-05
ro.build.version.base_os=
ro.build.date=201710101940
ro.build.date.utc=1507635652
ro.build.type=user
ro.build.user=jenkins
ro.build.host=ubuntu
ro.build.tags=release-keys
ro.build.flavor=full_lcsh8735m_6_co-user
ro.product.model=Lenovo TB3-850F
ro.product.brand=Lenovo
ro.product.name=LenovoTB3-850F
ro.product.device=TB3-850F
ro.product.board=TB3-850F
# ro.product.cpu.abi and ro.product.cpu.abi2 are obsolete,
# use ro.product.cpu.abilist instead.
ro.product.cpu.abi=arm64-v8a
ro.product.cpu.abilist=arm64-v8a,armeabi-v7a,armeabi
ro.product.cpu.abilist32=armeabi-v7a,armeabi
ro.product.cpu.abilist64=arm64-v8a
ro.product.manufacturer=LENOVO
ro.product.locale=en-US
ro.wifi.channels=
ro.board.platform=mt6735m
# ro.build.product is obsolete; use ro.product.device
ro.build.product=TB3-850F
# Do not try to parse description, fingerprint, or thumbprint
ro.build.description=full_lcsh8735m_6_co-user 6.0 MRA58K 1507635241 release-keys
ro.build.fingerprint=Lenovo/LenovoTB3-850F/TB3-850F:6.0/MRA58K/TB3-850F_S100031_171010_ROW:user/release-keys
ro.build.characteristics=tablet
ro.custom.external.version=LLD3I43.2.2_M007
ro.custom.internal.version=LLD3I43.1.0.2.2T31A1010_M007
ro.build.in-version=LLD3I43.1.0.2.2T31A1010_M007
ro.build.ex-version=LLD3I43.2.2_M007
ro.build.device.ninur=64687
ro.product.ota.model=LenovoTB3-850F_ROW
ro.com.google.clientidbase=android-lenovo
ro.com.google.clientidbase.ms=android-lenovo
ro.com.google.clientidbase.yt=android-lenovo
ro.com.google.clientidbase.am=android-lenovo
ro.com.google.clientidbase.gmm=android-lenovo
persist.gsensor.encali=1
ro.lenovo.series=Lenovo TAB3 8
ro.lenovo.software.version=TB3-850F_171010
ro.lenovo.hardware.version=LenovoPad TB3-850F
ro.custom.product.version=TB3-850F_USR_S100031_1710101940_MPM0._ROW
ro.lenovo.region=row
ro.lenovo.device=tablet
ro.lenovo.tablet=wifi
ro.lenovo.sim=none
ro.lenovo.operator=open
ro.lenovo.platform=mtk
ro.lenovo.bqb=pass
ro.lenovo.wificert=no
ro.lenovo.signalbars=four
ro.lenovo.videocall=false
ro.lenovo.cta=false
ro.lenovo.vibeuistyle=false
persist.sys.backgrounddata=true
persist.sys.lenovo.ltetype=NONE
ro.lxf_lenovo_standard_usb=1
ro.lenovo.audioparaver=V0.2
ro.lenovo.lvp.version=V1.0
ro.lenovo.batterysieze=4290
ro.lenovo.lcdsize=8
ro.lenovo.cpuinfo=MT8735P,4,1.0
ro.mtk.project=lcsh8735m_6_co
# end build properties
#
# from device/lcsh/lcsh8735m_6_co/system.prop
#
#
# system.prop for generic sdk
#

rild.libpath=mtk-ril.so
rild.libargs=-d /dev/ttyC0

# MTK, Infinity, 20090720 {
wifi.interface=wlan0
# MTK, Infinity, 20090720 }

# MTK, mtk03034, 20101210 {
ro.mediatek.wlan.wsc=1
# MTK, mtk03034 20101210}
# MTK, mtk03034, 20110318 {
ro.mediatek.wlan.p2p=1
# MTK, mtk03034 20110318}

# MTK, mtk03034, 20101213 {
mediatek.wlan.ctia=0
# MTK, mtk03034 20101213}

#
wifi.tethering.interface=ap0
#

ro.opengles.version=196608

wifi.direct.interface=p2p0
dalvik.vm.heapgrowthlimit=128m
dalvik.vm.heapsize=256m

# USB MTP WHQL
ro.sys.usb.mtp.whql.enable=0

# Power off opt in IPO
sys.ipo.pwrdncap=2

ro.sys.usb.storage.type=mtp,mass_storage

# USB BICR function
ro.sys.usb.bicr=yes

# USB Charge only function
ro.sys.usb.charging.only=yes

# audio
ro.camera.sound.forced=0
ro.audio.silent=0

ro.zygote.preload.enable=0

# temporary enables NAV bar (soft keys)
qemu.hw.mainkeys=0

ro.kernel.zio=38,108,105,16
#ro.kernel.qemu=1
#ro.kernel.qemu.gles=0
#ro.boot.selinux=disable

# Disable dirty region for Mali
debug.hwui.render_dirty_regions=false

ro.sf.lcd_density=213

# performance
ro.mtk_perf_simple_start_win=1
ro.mtk_perf_response_time=1

#runin test
ro.build.device.ninur=64687
#
# ADDITIONAL_BUILD_PROPERTIES
#
ro.config.alarm_alert=New_Morning.ogg
ro.config.ringtone=Fantastic_Clang.ogg
ro.config.notification_sound=Notice.ogg
ro.config.msg_notification=Bump.ogg
ro.carrier=unknown
dalvik.vm.heapgrowthlimit=128m
dalvik.vm.heapsize=256m
ro.mediatek.chip_ver=S01
ro.mediatek.version.release=alps-mp-m0.mp1-V2.39.1_lcsh8735m.6.co_P54
ro.mediatek.platform=MT6735
ro.telephony.sim.count=2
persist.radio.default.sim=0
persist.radio.multisim.config=ss
*ro.mtk.dex2oat_white_list=com.facebook.katana:
persist.gemini.sim_num=1
ro.gemini.smart_sim_switch=false
ril.specific.sm_cause=0
bgw.current3gband=0
ril.external.md=0
ro.sf.hwrotation=0
curlockscreen=0
ro.mediatek.gemini_support=false
drm.service.enabled=true
fmradio.driver.enable=1
ril.first.md=1
ril.flightmode.poweroffMD=1
ril.telephony.mode=0
dalvik.vm.mtk-stack-trace-file=/data/anr/mtk_traces.txt
mediatek.wlan.chip=CONSYS_MT6735
mediatek.wlan.module.postfix=_consys_mt6735
ril.radiooff.poweroffMD=0
ro.frp.pst=/dev/block/platform/mtk-msdc.0/11230000.msdc0/by-name/frp
ro.sys.usb.storage.type=mtp,mass_storage
ro.mediatek.version.branch=alps-mp-m0.mp1
ro.mediatek.version.sdk=4
ro.setupwizard.mode=OPTIONAL
ro.com.google.gmsversion=6.0_r2
ro.com.google.clientidbase=android-lenovo
ro.com.google.clientidbase.ms=android-lenovo
ro.com.google.clientidbase.yt=android-lenovo
ro.com.google.clientidbase.am=android-lenovo
ro.com.google.clientidbase.gmm=android-lenovo
ril.current.share_modem=1
ro.mtk_audio_profiles=1
ro.mtk_audenh_support=1
ro.mtk_bessurround_support=1
ro.mtk_bt_support=1
ro.mtk_wappush_support=1
ro.mtk_audio_tuning_tool_ver=V1
ro.mtk_matv_analog_support=1
ro.mtk_wlan_support=1
ro.mtk_ipo_support=1
ro.mtk_gps_support=1
ro.mtk_search_db_support=1
ro.mtk_dialer_search_support=1
ro.mtk_dhcpv6c_wifi=1
ro.have_aacencode_feature=1
ro.mtk_widevine_drm_l3_support=1
ro.mtk_fm_recording_support=1
ro.mtk_audio_ape_support=1
ro.mtk_flv_playback_support=1
ro.mtk_mtkps_playback_support=1
ro.mtk_send_rr_support=1
ro.mtk_emmc_support=1
ro.mtk_tetheringipv6_support=1
ro.mtk_shared_sdcard=1
ro.mtk_flight_mode_power_off_md=1
ro.mtk_pq_support=2
ro.mtk_miravision_support=1
ro.mtk_miravision_image_dc=1
ro.mtk_wifi_mcc_support=1
ro.mtk_sim_hot_swap=1
ro.mtk_thumbnail_play_support=1
ro.mtk_bip_scws=1
ro.mtk_cmcc_ft_precheck_support=1
ro.mtk_world_phone_policy=0
ro.mtk_perfservice_support=1
ro.mtk_audio_change_support=1
ro.mtk_owner_sdcard_support=1
ro.mtk_sim_hot_swap_common_slot=1
ro.mtk_cam_mfb_support=0
ro.mtk_subtitle_support=1
ro.have_aee_feature=1
ro.sim_me_lock_mode=0
ro.mtk_dual_mic_support=0
ro.mtk_is_tablet=0
wfd.dummy.enable=1
ro.mediatek.project.path=device/lcsh/lcsh8735m_6_co
persist.mtk.wcn.combo.chipid=-1
service.wcn.driver.ready=no
service.wcn.coredump.mode=2
ro.com.android.mobiledata=false
persist.radio.mobile.data=0,0
persist.meta.dumpdata=0
ro.mtk_deinterlace_support=1
mtk.vdec.waitkeyframeforplay=1
ro.lct_country_info_ctrl=1
ro.delete_all_recent_apps=1
ro.multi_mode_support=1
ro.lct.cetest=1
ro.lenovo.lowbattery_shutdown=1
ro.lct_show_time=1
ro.lxf_ip_call_support=0
ro.lxf_p3582_a01=1
ro.lxf_p3582_a02=0
ro.lxf_p3582_c01=0
ro.lxf_p3582_d02=0
ro.lxf_p3582_d04=0
ro.lct_lenovo_service_framwork=1
ro.lct_poweronff_same_anim=1
ro.lxf_p3582_pl=0
ro.lxf_p3582_p4=0
ro.qq.camera.sensor=3
persist.sys.dalvik.vm.lib.2=libart
dalvik.vm.isa.arm64.variant=cortex-a53
dalvik.vm.isa.arm64.features=default
dalvik.vm.isa.arm.variant=cortex-a53
dalvik.vm.isa.arm.features=default
net.bt.name=Android
dalvik.vm.stack-trace-file=/data/anr/traces.txt
ro.expect.recovery_id=0xf664de513a45ad6ac659647b77015289a9d815bb000000000000000000000000

Hope it helps, PW.