Pressing "0" for RAM preview only plays a few frames on my iMAc

Hi guys. I use CC at work, and as such I am also allowed to install an extra version on my iMac (late 2014) at home. Great! So I am following some training on LinkedIn Learning, and they refer all the time to the RAM Preview ... which works perfectly on my office computer (a pc).

The thing is, the RAM Preview worked just fine when I installed AE on my mac, but all of a sudden it will only play a few frames. I checked youtube, and there are a lot of suggestions there that I have tried, but none have worked so far. Mostly they referred to setting the cache and memory use, to try and adjust the Preview panel ... and none have worked so far. Does anyone in this excellent community have a clue to what I can try?

I attach a short video to show what I mean, and a screen clip of my mac's "about this mac."

Hope someone can help me out.

Best regards from Bent, Norway.