Well, I let it run all day today, and it looks like its still having the same problem. It is transmitting fine, as aprsdirect.com shows that my station was heard 3 mins ago by my nearest digi. But the last time any station heard me (including that same digi) was around noon (pasting below, if this works):
Stations that heard KE4DHK-10 directly during March 2018.
Stations directly heard by KE4DHK-10 during March 2018.
I looked at the log file, and my novice eye does not see anything obvious. I'd be glad to email the log file to someone if you're willing to look. Otherwise, I'm at a loss of what else to try.