United Brachial Plexus Network

my son Lbpi crawled normally at 7mos and for 2 mos now has had no problem open palmed, not fisted,etc. I noticed 4 days ago that once in awhile he will have his thumb under and since this is new, I was wondering anyone else have the same thing happen? If so, suggestions, a different exercise? He's never had surgery and otherwise has been right on time with everything and doing great. Thanks in advance