OK, I recorded midi under these similiar conditions for the a half hour or so. Using MME with no significant issue with latercy (likely because of how I playkeys - the original slow hand).
I set up 12 bars x 3x using RD's and Piano MST and Bass RT. Played and recorded fine. No crashes.

It does appear you may have the Pianoteq VST on two channels - on the thru so that you hear it play, and then on the Melody in order to playback the recorded midi. this worked fine on my machine, but may be stressful for your system? I suggest you just put default Synth on the thru to lighten the CPU load during recording.

Dan, BIAB2024, SoundCloud Win11, i7(12thGen), 32GB, 1TB SSD(M.2 NVMe SSD), 2TB Libraries, 1 TB(WD-Black), 2TB SSD(M.2 NVMe SSD)Data, Motu Audio Express, Keystation 61, SL88 Studio, Reaper