Chat apps not working in the background means that something broke the core gapps package and it's not working properly.
The only way sadly is to go into the stock recovery and wipe data. It will be like booting a new phone again.
But with the rom you have flashed
Hi guys! I'm the author of the First Ever Android 9.0 for Nexus 5 project (probably the best Android 9.0 for Google Nexus 5). The letters UBR stand for Update By Recovery - this is a very non conventional way of flashing
Unlocked Bootloader. You can get a key for €30, I received my key in 3 hours [Link]
TWRP 3.2.1-0 for Huawei P20 Pro working with Android 9.0
Remove Storage Encryption - flashable zip file
UBR (Update By Recovery) - one button installation like for Nexus 5!
1. Restore EMUI 8.1 via Huawei eRecovery [DONE] in 14:38 s
2. Wipe data/factory reset [no required?] [SKIP] in -:-- s
3. First EMUI 8.1 boot [DONE] in 0:58 s
4. Install TWRP via Fastboot [DONE] in 0:01 s
5. Install Remove_Encryption.zip via TWRP [DONE] in 0:03 s
6. Reboot to TWRP and Format Data [DONE] in 0:04 s
7. [UBR] First Ever Android 9.0 via TWRP [DONE] in 0:51 s
8. First AOSP 9.0 boot [DONE] in 0:35 s
Progress is updated live!
Is Evira Kernel still installed? [Yes]
Is Magisk 17.3 still installed? [Yes]
Are mods still installed? [Yes]
Are Magisk modules still installed? [Yes]
Is it possible to sign into Google account? [Yes]
Step-by-step installation guide and files will be released this week!
I'd like to clarify one thing: From the Opening Post, i see that it is necessary to have a P20 Pro running Android 9.0 to be able to flash this.
Is everyone here already running 9.0? If so, did you achieve this through a beta or did you flash 9.0 through TWRP or other method? I'm trying to figure out how to achieve this so i can be ready when this wonderful ROM drops
No, you are wrong. You can upgrade from any stock or custom ROM, for example from stock EMUI 8.1 to AOSP 9.0. If for some reason you do not like Android 9.0, you can downgrade to stock EMUI 8.1 by just one click in Huawei eRecovery