Beach ball appears a lot after some time editing

Hi, I'm running Final Cut Pro on my iMac 5K 2017 and MacBook Pro 13" 2020 (10th gen quad core i5, 16GB RAM, 512GB SSD, Intel Iris Plus graphics) using the same library on both devices.

I have enabled the background renderer and the "Better quality" option on both devices.

On the iMac, Final Cut works great all the time, but on the MacBook Pro, at about first 30 minutes of editing it works great as well but then it starts showing the beach ball very often even when doing very basic things like trimming etc. If I close and reopen FCP the performance is great again until the beach ball starts appearing again.

This happens in every 4K project (even new ones created on the MacBook Pro). Of course I have plenty of space available on the SSD (almost 300GB)

Any solution?