Possible valve issue or Other???

I've moved my lawn a few times already this season with the engine running just fine and this past weekend was mowing again as usual. I ran out of gas, refilled and upon trying to restart it, I couldn't get it to start... cranking just fine but as if still out of gas. I removed the gas line into the carb. and verified gas was flowing from line. I re-connected the line to the carb and tried again and it fired right up. However within about 30 seconds after starting, the engine acted like a heavy strain was on it, almost like a bearing was seizing up. I turned it off immediately and it stopped spinning abruptly (as opposed to a second or 2 to wine down to a stop as usual). I tried cranking it over again and it wouldn't even spin. As if A. the battery was dead, or B. a bearing was seized. I charged the battery full and then removed the plug and tried cranking again. It was spinning as it should. Yay, not seized!!! Replaced the plug and tried again, with a VERY difficult time turning the flywheel, as if a battery with a low charge barely spinning the engine, but know that's NOT the issue. OK, next possible issue could be a compression issue. To back up a step, when the plug was removed and cranking the engine, NO gas sprayed out the spark plug hole as it usually did with other problems I was troubleshooting in the past. Removed valve cover and inspected... I do not possess feeler gauges to officially check them, but they did not seem overly tight nor loose. Reassembled everything and no change.
That's basically the extent of how far I got on my own. Does anyone have any suggestions on possible other problems? Or if it is a valve problem, how could it be running fine till running out of gas then so abruptly have the issue?
Any suggestions are appreciated.

Possible valve issue or Other???