We will definitely run SQL profiler, but we suspect that this issue is not SQL related. We saw this problem in two different environments (different customers and development environments). Even 2MB file is a poblem (multiple seconds execution time in AbpAuditLogs).
Basically, my stupidity. We moved the current database from a local environment to Azure and then created a new tenant with the connection string to this database. But the tenant id was different from the value in the new host environment.
Correct steps:
Of course, the version of an application (and database) has to be the same during migration.