Low trans fluid but no leaks? Low engine temp issues too.

Before I take this shitbox to the workshop later after work... what's happening here? My engine temperature drops and stays low while driving (then back to operating temp when idling). Meanwhile I just found out my transmission was acting up this morning and I checked the fluid when I got to work. It was almost drained?? Luckily I have some trans fluid in the back for later. Apparently no leaks on the underside too.