[Android Q&A, Help & Troubleshooting] alpsayin:
Did you go through any special method for this build? I tried to build this again and permission13 error is back...

07-27 14:21:12.400 343 343 D Magisk : resetprop: getprop [ro.crypto.state]: [unencrypted]
07-27 14:21:12.401 343 343 I Magisk : ** Initializing Magisk
07-27 14:21:12.402 343 343 I Magisk : * Creating /sbin overlay
07-27 14:21:12.411 343 343 I Magisk : * Mounting mirrors
07-27 14:21:12.411 343 343 I Magisk : mount: /sbin/.core/mirror/system <- /dev/block/platform/mtk-msdc.0/11230000.msdc0/by-name/system
07-27 14:21:12.412 343 343 I Magisk : link: /sbin/.core/mirror/vendor <- /sbin/.core/mirror/system/vendor
07-27 14:21:12.412 343 343 I Magisk : bind_mount: /sbin/.core/mirror/bin <- /data/adb/magisk
07-27 14:21:12.412 343 343 I Magisk : * Setting up internal busybox
07-27 14:21:12.468 346 346 D Magisk : client: connect fail, try launching new daemon process
07-27 14:21:12.758 350 350 D Magisk : client: connect fail, try launching new daemon process
07-27 14:21:12.758 350 350 I Magisk : Magisk v16.7_P13_27082018(27082018) logger started
07-27 14:21:12.768 346 346 I Magisk : Magisk v16.7_P13_27082018(27082018) daemon started
07-27 14:21:12.772 346 352 I Magisk : ** post-fs-data mode running
07-27 14:21:12.773 346 352 I Magisk : * Mounting /data/adb/magisk.img
07-27 14:21:12.804 346 352 E Magisk : mount /sbin/.core/block/loop08->/sbin/.core/img failed with 13: Permission denied
07-27 14:21:12.807 346 352 I Magisk : * Running post-fs-data.d scripts
07-27 14:21:12.807 346 352 I Magisk : * Running module post-fs-data scripts
07-27 14:21:12.807 346 352 I Magisk : * Loading modules
07-27 14:21:12.812 346 352 D Magisk : resetprop: prop [persist.magisk.hide] does not exist
07-27 14:21:12.812 346 359 I Magisk : * Starting MagiskHide
07-27 14:21:12.812 346 359 D Magisk : resetprop: deleteprop [persist.magisk.hide]
07-27 14:21:12.812 346 359 I Magisk : hide_utils: Hiding sensitive props
07-27 14:21:12.812 346 359 D Magisk : resetprop: prop [ro.boot.vbmeta.device_state] does not exist
07-27 14:21:12.812 346 359 D Magisk : resetprop: getprop [ro.boot.verifiedbootstate]: [orange]
07-27 14:21:12.812 346 359 D Magisk : resetprop: setprop [ro.boot.verifiedbootstate]: [green] by modifing prop data structure
07-27 14:21:12.812 346 359 D Magisk : resetprop: getprop [ro.boot.flash.locked]: [0]
07-27 14:21:12.813 346 359 D Magisk : resetprop: setprop [ro.boot.flash.locked]: [1] by modifing prop data structure
07-27 14:21:12.813 346 359 D Magisk : resetprop: prop [ro.boot.veritymode] does not exist
07-27 14:21:12.813 346 359 D Magisk : resetprop: prop [ro.boot.warranty_bit] does not exist
07-27 14:21:12.813 346 359 D Magisk : resetprop: prop [ro.warranty_bit] does not exist
07-27 14:21:12.813 346 359 D Magisk : resetprop: getprop [ro.debuggable]: [0]
07-27 14:21:12.813 346 359 D Magisk : resetprop: getprop [ro.secure]: [1]
07-27 14:21:12.813 346 359 D Magisk : resetprop: getprop [ro.build.type]: [user]
07-27 14:21:12.813 346 359 D Magisk : resetprop: getprop [ro.build.tags]: [release-keys]
07-27 14:21:12.813 346 359 D Magisk : resetprop: prop [ro.build.selinux] does not exist
07-27 14:21:12.813 346 359 D Magisk : hide_list: initialize...
07-27 14:21:12.813 346 359 I Magisk : hide_list add: [com.google.android.gms.unstable]
07-27 14:21:13.747 346 500 I Magisk : ** late_start service mode running
07-27 14:21:13.748 346 500 I Magisk : * Running service.d scripts
07-27 14:21:13.748 346 500 I Magisk : * Running module service scripts
07-27 14:21:55.549 3541 3655 F Adjust : PRODUCTION: Adjust is running in Production mode. Use this setting only for the build that you want to publish. Set the environment to `sandbox` if you want to test your app!
07-27 14:22:19.951 5432 5432 F Adjust : PRODUCTION: Adjust is running in Production mode. Use this setting only for the build that you want to publish. Set the environment to `sandbox` if you want to test your app!
07-27 14:22:35.885 346 359 I Magisk : proc_monitor: com.google.android.gms.unstable (PID=[6462] ns=4026534096)(PPID=[417] ns=4026534012)
07-27 14:22:52.339 7121 7121 F Adjust : PRODUCTION: Adjust is running in Production mode. Use this setting only for the build that you want to publish. Set the environment to `sandbox` if you want to test your app!
07-27 14:22:55.605 346 7216 I Magisk : hide_list add: [uk.co.santander.santanderUK]
07-27 14:23:30.892 346 359 I Magisk : proc_monitor: com.google.android.gms.unstable (PID=[9608] ns=4026534104)(PPID=[417] ns=4026534012)
07-27 14:23:31.797 346 359 I Magisk : proc_monitor: uk.co.santander.santanderUK (PID=[9653] ns=4026534105)(PPID=[417] ns=4026534012)
07-27 14:24:30.496 12375 12453 F HTTPRequest /android a6b5c5: Request start: 1532697870495
07-27 14:24:33.422 12375 12453 F HTTPRequest /android a6b5c5: Request end: 1532697873422
07-27 14:24:36.942 12769 12769 F Adjust : PRODUCTION: Adjust is running in Production mode. Use this setting only for the build that you want to publish. Set the environment to `sandbox` if you want to test your app!
07-27 14:24:45.153 12990 13031 F Adjust : PRODUCTION: Adjust is running in Production mode. Use this setting only for the build that you want to publish. Set the environment to `sandbox` if you want to test your app!
07-27 14:25:16.743 346 359 I Magisk : proc_monitor: com.google.android.gms.unstable (PID=[14903] ns=4026534124)(PPID=[417] ns=4026534012)
07-27 14:26:14.961 16784 16784 F Adjust : PRODUCTION: Adjust is running in Production mode. Use this setting only for the build that you want to publish. Set the environment to `sandbox` if you want to test your app!
07-27 14:26:19.800 346 359 I Magisk : proc_monitor: com.google.android.gms.unstable (PID=[17062] ns=4026534103)(PPID=[417] ns=4026534012)
07-27 14:26:42.406 18090 18090 F Adjust : PRODUCTION: Adjust is running in Production mode. Use this setting only for the build that you want to publish. Set the environment to `sandbox` if you want to test your app!
07-27 14:26:52.816 18611 18611 F Adjust : PRODUCTION: Adjust is running in Production mode. Use this setting only for the build that you want to publish. Set the environment to `sandbox` if you want to test your app!
07-27 14:27:16.836 346 359 I Magisk : proc_monitor: uk.co.santander.santanderUK (PID=[19790] ns=4026534122)(PPID=[417] ns=4026534012)
07-27 14:27:35.128 20236 20236 F Adjust : PRODUCTION: Adjust is running in Production mode. Use this setting only for the build that you want to publish. Set the environment to `sandbox` if you want to test your app!
07-27 14:28:01.584 346 359 I Magisk : proc_monitor: uk.co.santander.santanderUK (PID=[21402] ns=4026534088)(PPID=[417] ns=4026534012)
07-27 14:28:20.605 22097 22097 F Adjust : PRODUCTION: Adjust is running in Production mode. Use this setting only for the build that you want to publish. Set the environment to `sandbox` if you want to test your app!