I have a 2014 Valk with only 2500 miles on it. In the past few months, I have noticed that shifting has become much more difficult. Now I am not talking about the normal "clunk" into first gear or from first to second gear, I am talking about third, fourth and fifth. It almost seems like I have to "muscle" it into gear. At the start of the riding season, I changed my own oil using the regular Honda oil- not synthetic. I have been riding "Jap" bikes for 40 years- never had a problem whether I was using regular oil or synthetic. I searched the board to see if anyone had similar issues. Some people switched to synthetic just for a little smoother shifting. But my difficultly shifting seem much worse than that. A Gold Wing should shift like butter. Could a change to synthetic make that big of a difference? I can't believe a $17,000 dollar bike should have an issue like this. Hondas have always been very good to me.
Was thinking about you during my ride.
Usually there are 2 sources of the problem, oil-related (as these bikes share engine oil with the tranny) and clutch related. Check your oil level, make sure you are well above the minimum mark but at or below maximum, and check clutch fluid level.
The only thing I can suggest beyond that is to change the oil again. It is also possible that a plate our two got stuck while in storage for the winter.
Otherwise you'll have to have a tech test ride it and then look at more - slave cylinder, slave actuation rod, throwout bearing, drum, forks, etc. Could be anywhere.