PC only uses 50% of my RAM

I have 32 GB Ram installed in 2 16 GB Sticks.

This was working fine for a whole while but recently I realized that sometimes I experience slow downs sometimes when using the PC. Checking my task manager it shows me 80%+ usage of my RAM, but when I add the amount of memory used I only land at 80% of 16GB.

So I thought maybe one of my RAM get's not detected correctly anymore, is hardware reserved, died or whatever. That would be plausible.

However, first I checked directly in Windows in Systems -> 32GB are being detected, 31,2GB are usable (so apparently no hardware reserved)

I installed CPU-Z and checked there as well. It shows both slots working and running, so 32 GB there as well.

I then opened msconfig and checked if a max RAM was set for boot, but nothing there as well.

I then checked Bios - 32GB detected.

My OS is also 64 bit.

I would say Task Manager is just wrong, but as I said, I experience the slow downs/lags once memory usage gets close to 16 GB.

Does anyone have an idea whats going on here?