Did the same thing about three years ago. Went from no issues with deep water starts two boots to failing to get up three or four times before getting up. I know what I was doing wrong and just could not brake the bad habits. And yes it felt like my grip was lacking. In truth it was all technick. worked on it and its back to nearly never missing a start.
Yes I use clincher, Vice gloves and I also was getting heavy, no fat! So I fixed that also but after getting my starts down so size was not my biggest problem but sure does not help. I went from 255 to 210 lbs over the last two years and at 66 I am skiing my best ever!