There is precedent for hair growing slower after your 2nd HT.
Dr. Bernstein even reported on it: https://www.bernsteinmedical.com/answers/hair-growth-with-a-second-transplant/
Does Hair Grow More Slowly After a Second or After a First Hair Transplant?
August 24th, 2005
Q: This is my second hair transplant and is seems like it is growing more slowly than my first. Is this normal? – J.D., Port Washington, N.Y.
A: It is common for a second hair transplant to take a bit longer to grow than the first, so this should be expected. It is also possible that there is some shedding from the procedure, or a continuation of your genetic hair loss.
Propecia may be helpful in this regard. It is important to wait at least a year for the transplant to grow in fully and to give a chance for any hair that was shed to regrow