I started using an Inkbird this summer (Aussie summer that is). It's pretty good, but I also had issues with water getting in. First opened it when the batteries died, and saw why the batteries had died so soon. Batteries and water don't mix well.
I suspected that water might come through from the bottom, where the thermocouple couple with cables comes in. I filled the the bottom with a good blob of silicone to improve the sealing. I just got it out of the water again after two months or so and opened it, and it was completely dry on the inside. The silicone blob seems to have done it's job.
Just put it back into the pool, and also added two little desiccant sachets for additional peace of mind - great suggestion. Thanks to I don't know how many Covid-RATs for school testing, we have quite a collection of them now - I knew they'd come in handy at some point.