Why do you need to lock off strength in the first place?
What is a lock off?
How do you lock off?
The Three Second Lock Off Strength Drill: aka The Hover
This will require you to lock off with the arm/hand holding on as well as focus on foot placement and complex core strength. The route that used to be reasonable for you just got hard. Possibly really hard. Try this drill at least once a week when you climb after a warm up. Use it as what it is, training, its a drill designed specifically to train lock off strength applicable to climbing.