for the tasks that are not deleted, log is different:
[2021-09-09 12:19:07,718] [8] [WARNING] [clearml.service_repo] Returned 400 for tasks.dequeue in 4ms, msg=Invalid task id: status=stopped, expected=queued

We'll take a look

no new unremovable entries have appeared (although I haven’t tried)

And still happens?

log:
[2021-09-09 11:22:09,339] [8] [WARNING] [clearml.service_repo] Returned 400 for tasks.dequeue in 2ms, msg=Invalid task id: id=28d2cf5233fe41399c255950aa8b 8c9d,company=d1bd92a3b039400cbafc60a7a5b1e52b

this does not prevent from enqueuing and running new tasks, rather an eyesore

FiercePenguin76 , we'll try to reproduce. Thanks for the input!

I think they appeared when I had a lot of HPO tasks enqueued and not started yet, and then I decided to either Abort or Archive them - I don’t remember already

but the old ones are there, and I can’t do anything about them

FiercePenguin76 does this happen in a self-hosted ClearML Server? If so, what is the server version?

self-hosted. Just upgraded to latest version today (1.1.1). The problem appeared when we were still using 1.0.2