You may encounter Hondas equipped with manual transmissions where the trans pops out of gear and/or shifts stiffly.
This may very well be due to the use of old Honda manual transmission fluid (MTF) or some aftermarket MTF.
Try draining the fluid and replacing with new Honda Genuine MTF, P/N 08798-9031.
According to Honda, this new MTF offers better overall shift quality and cold weather operation, with better friction reduction.
After filling with the new MTF, take a 10-mile test drive that involves plenty of shifting. If it’s still acting up, it’s time to troubleshoot.