Can the harmonic balance come loose?

Myasylum - I agree with REDFISH, I have installed a balancer bolt which was too long and did not catch it at first. When I did this I used an impact wrench - BIG NO-NO, learned the hard way. Result, needed to re-thread and put in a smaller bolt. Recommendation would be to go to Harbor Freight and buy a low cost balancer puller, about $15, get some anti-seize also. Follow what REDFISH said, but be very careful. Once the bolt is off, find a mic and check the depth on the bolt, bolt should not go all the way to the bottom, threads stop before that and you want the bolt to go about 75% down the threads. If you messed up the thread, you can get a tap from Summit and run it down, with anti-seize. You can probably do all this without pulling the balancer. I used a propane torch to heat the bolt to remove it when mine was on very tight, again watch you seals, anything rubber, overheating the snout etc. When you re-install the the bolt use a lot of anti-seize. I do think this is the issue, if they used an aftermarket crank with the factory bolt and with signs and symptoms you stated and showed, this is from my experience.

If the thrust was the case or something was broken, your signs are subtle. Easy fix, step away, have a coke and enjoy.