Telesin waterproof case issue

I like these cases, and they worked the first time we snorkeled with them in the ocean, but in a saltwater lagoon, the second time we used them, both of them fogged up like this. Is this actually fog or something else?

I found it weird that it happened to both cameras, especially since I used the moisture absorbing inserts. I haven’t reused any of them after the first use, but that’s another question I have - can you reuse them?

The blindspot grew to this size gradually over the course of 20 minutes to half an hour. We’re using DJI Action 4’s. I don’t know if I fully trust the buttons that allow you to stop a video and start a new one to be fully waterproof, but we did use them.

Any information on this would be greatly appreciated! I really love these cameras, but don’t know if I should stick with the Telesin cases or get the name brand version…