Transmission becomes stuck in gear while riding.. can pop out temporarily & get stuck in another gear

[The Organic Mechanic]

So I got my bike running well after adjusting the valve clearances and installing a new to me FCR39MX, however it has developed the problem of getting stuck in gear on the test rides since I got it running. At first it was stuck in 5th gear, I managed to clutch it up to speed and get her home, where after awhile my dad was able to get it out of gear, He took it for a little spin and it got stuck in 3rd gear, came out at some point and was stuck in 2nd gear. 

Anyways, wasn't much data about where to start with this from my searching. It appears that this could be caused by debris that fell into the bottom end during the valve clearance adjustment? Maybe a loose valve shim would be the right little bugger to gum up the transmission? Any recommendations for where to begin my hunt? Take off the side case? It's worth noting that the cam chain had been stuffed into the bottom of the motor, while the motor was turned, however we were able to free it up and get the clearances in order. Somewhere in that stupidity, something went wrong that is allowing the transmission to get locked up in gear. 

[habs]

had same problem few weeks ago , stuck in fifth gear , followed some advise from TT members , open  right case cover and check external shift mechanism , my problem was a stuck spring on one pawl , probably dirt , changed both spring and pins , working fine now but you need a clymer book unless familiar with this stuff , first picture you can see top  pawl not engaging cam , second picture is how it should be . 

[habs]

https://www.thumpertalk.com/forums/topic/1225454-stock-in-forth-gear/#comment-13684984