Do not ever assume your watch is waterproof after you have opened it yourself, even if it looks all fine to you.
If it does not close well: make sure you have the exact right fitting screwdriver, open it up again, verify all ribbon connectors are seated properly, photograpgh every step, patiently lay down the gasket again, carefully place back the back cover, tighten screws lightly, first one and then the opposite corner, other 2 same, verify everything works (HR lights, charging, data transfer, clock functions, GPS, phone connection, backlight, buttons, buzzer) then tighten them properly. And don't use it under water or in the shower. Better safe than very sorry.
I already used it in the sea for 3 days and it worked perfectly in the water and capture eveything. Even if screws not very tighthened after i ooen and close it. It worked. Only problem i have nove is charging problem because of having corrosion on the pin need to check if some chemicals is suitable for clean the corrosion.
For charging problem I have ordered Isopropyl alcohol and use it with Q-tip. Cleaning he charging tips around one minute and then it works perfectly.
So as a summary, I have open the back case and close it after closing the back case I realise that screws can not be tightened and they are turning like they are worn.
I was not sure if it is still waterproof. I decided to swim with my watch to see the result and 3 days I swam with Garmin fenix 5 plus and It works perfectly. Only problem remaining was charging problem which I already metion the solution was Isopropol alcohol and q-tip. I hope this will help someone having similar problem now or in the future.
