I'm not clear why you are shooting 1920 x 1080 (1080p) 30fps of a 4K camera at medium quality. I'm sure you have your reasons.
The first thing I would try is a different memory card perhaps at least 64 GB or even 128 GB and use something other than the EVO PLus. The Maxi 4K may not like the Samsing EVO PLUS. This may be more than you need but it "may" fix your problem.
Then I would try different settings. Have you tried shooting at different resolutions? You should. See what happens. Try the default 4K the camera was built for, for example, and then other resolutions. Same with video quality. Troubleshooting is a process of elimination, so try one step at a time and then change the next parameter.