Hello and welcome to the forum.
I saw this same question you posted at forum X
and I know from past experience that you don't get a lot of response there.
It's always hard to diagnose these kinds of problems based on descriptions.
However, if it was me, I would remove the inner and outer clutch cover and take a look at the shift cam asy.
Look for anything that is out of place or clearly worn.
Have someone rock the bike gently and shift the gears while you watch the mechanism and see if you can see something.
If that does not pan out your down to splitting your cases and looking for broken snap rings on the transmission shafts, worn or broke dog ears on the gears, worn or bent shift forks, worn, shift drum.
Do you have a Service manual for your bike?
If not, it would be a good idea to get one before you start tearing into things
Keep us informed and post pics as it really helps us see what you have going on.