Questions not loading when a unit contains multiple Randomize content blocks

I’m using tutor v16.1.7.

I created a unit and 4 Randomize Content Block (RCB) in it.
For each RCB I set the number of questions to 5.
When I published and loaded the unit in LMS, only the first RCB loaded, and the last 3 didn’t.
The error might not happen if I try to clear caches or open in incognito mode, so I guess it was caches cache-related problem.
This happened in Safari and Chrome, Firefox didn’t have it.

Browser logs.