It's converting HBD (since HBD is below peg), which takes 3.5 days, so that part of the funds is "missing" for 3.5 days. Once the conversions complete the HIVE will be returned to DHF which, on average, should yield a profit. Unless HBD remains below peg in which case it will convert again, repeating the above process.

is the bot not buying on the internal market anymore after HF25, just conversions back and forth?

It buys when it has HIVE if HBD is below 1 USD.

It doesn't always have HIVE though, since all payments from DHF are in HBD. To be in a position to buy HBD, it has to get HIVE from a conversion, from selling HBD, or a power down (or HIVE donation).

Also, I'm curious what you are using to track the balance over time.

Just the top of the proposal page on peakd. I check it once a day and it has been steady increasing, but stopped a few days/weeks ago. I just saw now the huge amount of pending conversions...