I wouldn’t be so optimistic regarding fast tracking the problem down.
it seems that very similar issue with rb4011
http://forum.mikrotik.com/t/rb4011-wlan1-disabling-itself/125605/1
was reported in dec’18, and in april’19 first response from Mikrotik staff that they recognise problem and working on solution,
and it seems that they haven’t solved it till now.
maybe there is some serious flaw in hardware, as we see it above
Unfortunately, this problem seems to be caused by a hardware issue.
Please contact the seller and return the router for warranty repairs, if the router is still covered by it. You can refer to this ticket number - SUP-3012.
either the way i’ve got my winbox opened on my problematic 4011 and 7d12h uptime. maybe winbox opened does the trick? I doubt it but whatever, when it works.
Merry Xmas 