Why does my A7 2017 have trouble in FHD underwater??

Hello everyone, i am new to smart phones all together.
So, i have tested the Sam A7 2017 submerged by maybe 10 to 20 cm's under water to flm myself swimming (swim style correction study) but when i try this in fullHD mode, no matter if i use the front or rer camera for this, it turns itself off after just a few seconds under water, with a note being displayed saying something like (can not zoom in or out in this mode).

I have zero clue what this means, anyone in the knowing here??

When i switch down to the next lower resolution, 1x1, about 1050x1050, it does not do that, but, of course, the video is square and not as great as it would be in FHD in the regular format.

I have seen people posting videos online taken over and under water at pools and they did not seem to have this problem.
I also tried to take a video while i hand hold the smartphone and i got at least one in FHD working this way - the other way i do it is when i either tie a rope around the smarty and hang it from the jump block, or use a special plastic bag where i cut out the camera sections, and that is certainly when this "can not zoom in or out in this mode" happens.

Any help welcome and wanted, but please, don't tell me this device is not made for underwater videos because it is supposed to be capable thereof as the IP68 indicates, 150cm max and 30 minutes, which i did not infringe, and everything else works just fine, all i have to do is make sure i blow out the 3 ports, speaker, USB and headset to ensure no humidity stays in there afterwards...