[G3 Q&A, Help & Troubleshooting] ninikninik:
If you upgraded ROM in jagnm probably You have broken WiFi that cant connect to almost any hotspot. Check wifi advanced setting for mac - it's 00:00:00:00:00:00

I tried several ROMs - all except factory ROM had this issue. Going back to stock ROM on that device is bad idea, it's old and packed with bulky apps.

Finally I decided to go with unofficial lineage os 15.1 from here: https://vasy.ru/LineageOS-15/jagnm/

Rooted that with supersu, and started console (you can enable it in developer settings or use "adb shell" command from pc - that is more comfortable to write anything).

in console enter su, then bash, and check interfaces:

C:\adb>adb shell
* daemon not running; starting now at tcp:5037
* daemon started successfully
jagnm:/ $ su
jagnm:/ # bash
jagnm / # ifconfig
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
(...)

wlan0 Link encap:Ethernet HWaddr 00:00:00:00:00:00 Driver bcmsdh_sdmmc

(...)

jagnm / #

in file /data/misc/wifi/config You will find that cur_etheraddr is set to all zeros,

jagnm / # cat /data/misc/wifi/config
btc_mode=1
mpc=1
roam_off=0
roam_scan_period=10
roam_delta=20
roam_trigger=-80
PM=2
cur_etheraddr=00:00:00:00:00:00

changing that line to anything restores wifi mac address on next interface restart, let's try:

jagnm / # sed -i "s/00:/11:/g" /data/misc/wifi/config
jagnm / # ifconfig wlan0 down
jagnm / # ifconfig wlan0 up
jagnm / # fconfig wlan0
wlan0 Link encap:Ethernet HWaddr 00:90:4c:c5:12:38 Driver bcmsdh_sdmmc
inet addr:192.168.1.251 Bcast:192.168.1.255 Mask:255.255.255.0
inet6 addr: fe80::290:4cff:fec5:1238/64 Scope: Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:108 errors:0 dropped:0 overruns:0 frame:0
TX packets:32 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:20601 TX bytes:3720

Any change to that line helps to restore original mac address, You can also delete this file chmod it or directory to something unreadable, but it will be recreated to zeros on each restart and problem will come back. I needed to find a way to fix that permanently, I looked for any startup scripts but it seems that init_d is not working on lineage, I followed that guide to fix that: https://xdaforums.com/lineage/general/how-to-enable-init-d-to-function-t3810355

With init_d there is script here: /etc/init.d/90userinit that looks for userscript here: /data/local/userinit.sh so let's put there same thing as above

jagnm / # echo 'ifconfig wlan0 down && sed -i "s/00:/11:/g" /data/misc/wifi/config && ifconfig wlan0 up' > /data/local/userinit.sh
jagnm / # chmod +x /data/local/userinit.sh

this will fix wifi mac on each restart. Of course You need to make all those each time You flash new rom, but it's not that frequent on so old phone with almost no updates. Probably I'll never use any sim card here, but wifi is best way to have internet on this device.

I hope that will help, it's old device and probably noone use that as main phone - with working wifi You can still find something to to for this device in home.

please report if this fixed problem on your lg g3s, what is Your ROM or if You have anyt other idea how to fix that config generating all zeros for mac address