ROS has quite a few built in tools for troubleshooting/debugging. In this 2017 Mum presentation, starting on page 34 are some examples. However, it is from 2017, and v6.38.5 from 9 years ago. So some details may be different. Basic guidelines on RouterOS configuration and debugging - Martins Strods, April 2017.
I recently saw a link to the mikrotikdocs.fyi site, and it is for v7 and in general is easier to follow than the official docs. But it is for ROS only, there is nothing about SwOS there (yet anyway). And your CSS318 is SwOS only. So do see the Official docs for it here CRS3xx and CSS3xx series Manual (SwOS).
You report some odd problems, like: "when I connect to my master wifi SSID… it works… once. When I reconnect, I don’t get an IP anymore." Sniffer on the CAP may be helpful, as would a wireshark capture on the wifi client.
And this is odd too "Taking out the second hAP helps to be able to connect with the fourth SSID. But if I reconfigure this hAP as an AP, it can’t connect to the CAPsMAN anymore. Comparing the script of both situations isn’t enlightening." I have never used any MikroTik wifi devices, so I am not going to be a good source of info about that.
However, as DuctView said, trying to simplify to the simplest config that still shows the problem and reporting that will be more likely to get useful feedback than than a complete dump without any info.
And a diagram of how things are connected is really useful to transfer info about how things are connected. Even a photo of a hand drawn sketch is much better than a bunch of words describing the connections. And the export of the config is going to be needed at some point, but there is still a lot of info that is needed along with an export, without context if is hard to know if a config is "correct" for the intended purpose.