Yes it is perfectly normal. As you progress in strength your programming needs to be more and more complex.Or is it normal to make gains for six months and then plateau?
I think getting back to lifting 2 x week is a good idea if you can manage it recovery-wise. I'd make the 2nd day a light(er) one, for instance 2 sets of 5 @80% of your standard working weight. Eventually in the future you might need to reset, cut the weights by 10% and build back up from there.
Hope that helps! Good luck with your training!