Hey @Steven Caldwell
A few were regarding the un-maintained nature of the house.
-Both bathrooms ended up with excessive mold in wall cavities, requiring mold remediation and reframing.
-Sewer lines had roots in the line, causing a whole house flood (luckily only concrete subfloor at that moment). (Emergency Plumber services are expensive and predatory was a secondary lesson there)
-Also we ran into drainage pipes in the concrete that were not connected to each other, just a pipe within a pipe, for which we had to jackhammer out a make a proper connections in order to prevent flooding in the event of backpressure from clogged lines.
-Some bad ceiling joists called for reinforcing and new sheet rock.
Then there are your typical first time investor mistakes;
-Remodeling the property too nice for the future rental use.
-Scope creep.
-Taking on too much work yourself instead of budgeting in a crew to do work efficiently on and schedule.
-Insurance okay'd the purchase of the house, but right after closing, threated to terminate coverage unless a 80' mulberry was removed from next to the house. (That was an expensive tree to have cut down within a week.)
Those are just a few that come to mind at the moment. But you will have to forgive me, this house was remodeled 2017-2018, and I am blanking on some of the other problem items that popped up during the rehab. We did also replace all mechanicals.
I hope that somewhat answers your question.