It used to be that when someone would surprise me with a lob that I would forget to change grips. I’d clutch on to my forehand grip and be so worried about getting into position for the overhead, that I’d forget to change to the continental or serving grip.
A simple drill you can do in your living room is to hold your forehand or backhand grip and then simply imagine a lob is hit to you.
Look up, . . . . back up and . . .switch your grip.
Do this a couple hundred times a night for a month and I guarantee you that you will never forget to change grips when you’re faced with a surprise lob.
Also, note that the same tip will work if you forget to switch grips when attacking the net after an approach shot. (Just don’t whack a lamp in your living room when simulating the approach shot.)