I'm not sure what's going on, but it seems like my builder and my scien…

I'm not sure what's going on, but it seems like my builder and my scientist are stuck at adept status. They say they improve in construction or research, but there is no noticeable change in their bar. I've tried this at all speeds. Does it just take a reeeaally long time to master a skill? Another of my villagers is a master scientist already while the other two are slacking.

Thanks!