After rolling back to 18.211.4 things have stabilized again. Next steps is to try 19.1.4 again and see if the issues return.
Guess it would help if I gave some additional information on the setup a well.
Topology ISP 1 (1G) - ISP 2 (1G) --> MX75 --> L3 VLAN --> Unifi 10GB switch L3 VLAN --> Multiple VLANs over multiple ports --> MR 44 1 - MR 44 2 --> Clients wired - Wireless.