Unsolved C64 emulator runs slowly on Raspberry Pi Zero W

[pszajow]

I have just started to play with Recalbox on Raspberry Pi Zero W placed in GPi CASE (the first version). I downloaded the current version of Recalbox from this link https://upgrade.recalbox.com/latest/download-wizard/rpi1/recalbox-rpi1.img.xz yesterday. Everything works fine, even some 3D games are playable (for instance the ones in "Ports" section) and the only problem is Commodore 64 emulation - it runns very slowly and the sound is breaking. I made sure, that I do have all necessary roms and I tried various changes in the configuration, but without reasonable guidiance I made things even worse.
BTW: I was running Vice emulator in a different setup on the same computer and it was running fine - with no delays and not problems with sound, so I guess, that this is some kind of configuration mismatch between Recalbox and Vice.
Question: how to investigate, what is the problem here? Which options should I check?