Server-based key backup recovery failed partially

I forgot my password while still having a session signed in on my phone.

To avoid losing my E2E encrypted messages, I enabled server based key backup using the recovery key option. I did so through settings - I had previously received a popup encouraging me to set up key backups, but that one required me to re-enter my account password. The backup showed up as successful.

I also exported keys just to be sure.

I then reset my password. (I think the web version told me to approve the session instead of asking for the recovery key.)
I signed in again on my phone, and entered the recovery key (I think again going through the settings).

Once I did that, it showed something like 12 keys restored. This allowed me to read my _sent_ messages, but not _received_ ones (these were showing the "unable to decrypt. the sender's device has not sent us the keys" message). Backing out of the chat and the app and reopening it did not fix that, so I don't think it was a transient error.

Only after importing the manually exported keys (which showed hundreds of keys imported) was I able to actually recovery my chat history.