AdMob crashes the iOS build on some devices

I got really weird case, which I can't reproduce on our tests devices (on 7 of iPhone devices) but I see crashes in FirebaseCrashlytics and BugFender remote logs.

I have no clue, what can be the reason...
Here is a short log

Code (CSharp):

1. Incident Identifier: CBCF0C86-AB4C-46C6-A2CA-E7F189ADCC12
2. CrashReporter Key:   518a8510dbc01f95ab5437c00933c9f2bb9a83d0
3. Hardware Model:      iPhone12,3
4. Process:         triviafight [2025]
5. Path:            /private/var/containers/Bundle/Application/FF120780-9500-4020-AF7C-FC99DFF74C89/triviafight.app/triviafight
6. Identifier:      com.triviagamesaps.triviafight
7. Version:         1.2.0 (26)
8. Code Type:       ARM-64
9. Parent Process:  ? [1]
10. Date/Time:       2020-09-10 10:00:26.000 +0100
11. OS Version:      iOS 13.6.1 (17G80)
12. Report Version:  104
13. Exception Type:  EXC_BAD_ACCESS (SIGBUS)
14. Exception Codes: 0x00000000 at 0x0000000000000000
15. Crashed Thread:  0
16.  
17. // ............ a lot of logs here
18.  
19. Extra Information:
20. Stack Dump (0x000000016d67f500-0x000000016d67f5f0):
21. 010000000000000060DFC5020100000040F5676D010000003C41B30501000000010000000000000000000000000000000000000000000000A0F5676D0100000090F5676D010000009C22950501000000B8F7C83A0100000000B02D020200000000006A070100000030222D0202000000C018F0810200000088339B070100000010C0FD0B0100000058F6676D0100000010F6676D01000000ECCC94050100000060DFC502010000000100000001000000000000000000000002000000000000000100000000000000384226F601000000B8F7C83A0100000000B02D020200000000006A070100000030222D0202000000
22. Application Stats:
23. {
24.     "active_time_since_last_crash": 0,
25.     "active_time_since_launch": 0,
26.     "application_active": false,
27.     "application_in_foreground": true,
28.     "background_time_since_last_crash": 0,
29.     "background_time_since_launch": 0,
30.     "launches_since_last_crash": 2,
31.     "sessions_since_last_crash": 2,
32.     "sessions_since_launch": 1
33. }
34. CrashDoctor Diagnosis: Attempted to dereference null pointer.

Full log is here

We use many 3rd party assets in the project like Native Pack plugins, Firebase, Facebook, IronSource etc..
Tried to google anything from readable data in the log - no success...
What else can I try here?

 

If someone experienced same issue here is a discussion + fix solution.
In a short - it's a Unity 2019.3 bug caused if app was terminated when any ad was shown. The crash is harmless and user doesn't see anything, but anyway, it's weird to see 20% of users had a crash