can you find any information in the SQLServer Errorlog file or in the cluster logfile ?

" ... just installed an instance of SQL 2017 and restarted the server.... "  
chances are, that may have reset the folder / file permissions.

Could you elaborate why these databases would be in recovery pending state ?
Apparently the SQLServer service account cannot access the folder E:\Databases

How did you configure the listener ?  ( TSQL / Posh script please )
Check your cluster logs !

what seeding setting do you currently have on your AGs ?
I've set it to "manual" once I have my AGs in a fucntioning state.

It seems to be OK now.
( I only receive the notifications because I follow Jeff )

I will let you know if it happens again.

Thanks

it got worse since last week.
So all these mails get into a "junk" folder and will not be processed at all.

That's a shame

even today I received feedback of a 3th party software taking its own log backups, breaking log shipping scenarios ...

You are missing some log backups !
Maybe someone created a log backup out of the normal sequence / location and your log-ship misses that file.
full backups do not...

Ever considered a trigger ( for insert / update / delete ) which checks your completeness and puts an extra column "TSAvailable' to current_timestamp, rolls back the insert/update if %...