Bulk events import - random errors in 2.34 - UID is not a valid data element


I am experiencing an strange error when importing lot of events through the API. The events are quite simple: 1 event per orgUnit with the same structure, containing only 1 value for the same dataElement in the program.

POST: /api/events?importReportMode=ERRORS&importStrategy=CREATE&async=true&preheatCache=false&skipExistingCheck=true

When doing a POST to the previous event endpoint and joining a json with hundred or thousand of events, almost all are being imported. But, randomly, 3 or 2 or 1 are raising the following error:

UID12345678 is not a valid data element

When deleting the events in the database and uploading the same json again, other events for other orgUnits are raising the problem.

The taskSummary looks like this:

And the global summary says:
Status: ERROR. Imported: 459. Updated: 0. Ignored: 2. Total: 461

When checking in the database, a programstageinstance is created, though without value:

select eventdatavalues from programstageinstance where uid = 'dFrwOK5EYtY';
(1 row)

Thanks for any idea/suggestion