Ohhhhh... ok. I had the same problem with DSLRs and RPi. The USB Bus on is shared (network for example) and is not capable
to cope with the large size of the files. That's my opinion but others using it can confirm. This also happens with dedicated OSC cameras.
Normally there are some options that have to be disabled so you can use it, even on an RPi4 because they are very demanding (Auto-debayer, 3D Cube).
You also have to enable "Limited Resources mode". I have opted with the same decision as you at the time, use the guider.
All this options are on the Fits options configuration, have you tried them?

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