Have you seen changes withing to 2 years with this issue?
Do you sit alot throughout the day?
Are you working up/down stream of the hamstring?

From an episode write up:
Sitting puts insertions of your hamstrings and adductors under serious passive stretch. Multiply this passive crappy loading by literally thousands of hours,
and make it gnarlier by the fact that you literally compress the crap
out of these bits and suddenly, poof, the devil lives in your sits
bones.

A few to check out.
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Pro Episode # 36 – Voodoo Floss Series # 3: The High Hamstring
High Hamstring Gnar, Trigger Points, and Up Stream/Down Stream
Episode 58: Weird Hamstring Problems and Simple Neurodynamics
Episode 104: Hammer Your High Hammy
Episode 105: Deadlift Prep
Episode 106: Deadlift Part 1

If you are working on glute/hamstring strengthening and not seeing change this is not where the issue originates.