Hi twolf and welcome to the Pool Forum. There is no such thing as chlorine lock. As far as still registering a chlorine level of 6 at the end of the winter, that is possible. Depends on what your levels were at closing. Do you have a good test kit? The only one we recommend is the Taylor K-2006 or 2006C which you can get through the Amazon link in my signature below. Only buy if the listed seller is Amato Industries as some other sellers ship the K-2005 instead which you do NOT want.

Post a complete set of current water testing results taken with a drops-based kit and make sure CYA is one of the tests you run. Also, tell us more about your pool, pump, filter. Then somebody here can better advise you.