ODK Aggregate - Data corruption error

1. What is the issue? Please be detailed.
Upon logging in onto our ODK-aggregate server, we receive the following error message: "Error: Encountered an unknown problem while reading the database. This often is a sign of database corruption. Please get the server logs and file an issue at https://github.com/opendatakit/aggregate/issues". The website still works, however, the message pops up everytime we go to the 'Filter submissions' page. I cannot select a filter or form (just shows a blank dropdown list). I can see export previous exported forms under 'Exported submissions'.

2. What steps can we take to reproduce this issue?
This problem started to appear since last Monday (27 May 2024).

3. What have you tried to fix the issue?
I searched for information on the Github website that was mentioned in the error message. Another user experienced a similar problem and the same error message earlier this year. One responded that it's better to ask for support on this forum, rather than open an issue on GitHub.
We host Aggregate on a Google Cloud Firestore (?) and suspect that the error is due to storage limitations. However, I am not familiar with ODK Aggregate or Google Cloud, so I'm a bit at a loss of where to start to figure out if this is indeed the case.
The server and Aggregate was created by our dedicated IT-person who unfortunately is ill and won't return to the office any time soon. It's therefore up to the other people with data affinity to solve this issue, but me nor someone in my team is familiar with the setup we use.

I am aware that ODK Aggregate is not supported anymore and we would love to transfer to ODK Central to get better support when issues like this arises, but are currently unable to do so while we cannot access the current database on Aggregate.

4. Upload any forms or screenshots you can share publicly below.

https://github.com/getodk/getodk/wiki/Aggregate-AppEngine-Troubleshooting has some ideas on how you could fix it, but it's been 5+ years since these instructions were written so they may no longer be correct or relevant.