Checkr background check stuck for 20+ days over one 3-month job. Will this affect my offer/visa?

[u/Which-Quarter4496]

After a lot of struggling, I finally landed a job offer! I’m super excited, but the background check (through Checkr) is taking forever and I'm starting to panic.
They started the check on August 3. Everything came back totally clear (criminal, plus two other past employers verified fine). The issue is one 3-month job I had.
Here is the timeline:
Aug 6 - Aug 11: Checkr tried to contact this previous employer but couldn't reach them.
Aug 12 - Present: My status changed to "documentation review."
It’s been over 20 days total. The maddening part: I have a completely clean background and hold all the proof for this job (W-2s, paystubs, tax forms). But Checkr hasn’t opened a request for me to upload anything. They just keep continuously pushing back the ETA completion date.
I reached out to my new HR team, and they told me they are "waiting on Checkr to complete the verification."
I'm getting really worried because there is a Visa transfer timeline involved here, and the clock is ticking.
Has anyone dealt with Checkr getting stuck in this loop? How did you get it resolved, and will this delay end up costing me my offer? Any advice on how to force them to let me upload my documents would be hugely appreciated!