My best guess is that your virus scanner tagged a hand and won’t install it, or deleted a file. I’d try temp turning your virus scanner off and re-installing. Make sure DH is loaded up before your MTT table is loaded to ensure capture. But the best way to know for sure is submit a log through the DH support icon (top right side in DH). This way we don’t have to guess and can tell you what’s going on exactly.
As far as your hand amount and switching time, that’s unusually long. I have ~1.2mill hands in mine and it takes about 4-5 secs on average to switch data points. I don’t have an exceptionally fast system or anything either. So something might be going on w/ your system space, available memory, or even database. But again, when you send a log we’ll know for sure.