I am getting this error both elementary OS 5.1 & Kubuntu 19.10:
Error while loading the metadata pool: Unable to add data: MDB_BAD_VALSIZE: Unsupported size of key/DB name/data, or wrong DUPFIXED size

Because of this problem AppCenter (eOS) & Discover (Kubuntu) package managers not working properly. They are not showing all apps.

My comprehensive bug report is here: elementary/triage#6