are you sure you didnt just recast her 4 at some point? bc it will only gain the extra duration if her 3 isn't already maxxed, so if you have a maxxed 3 and a new 4, her 4 wont get all that much extra duration. not uncommon to deal with doing stuff like relics, recasting for the str buff etc, but not really a bug or anything
been playing Gyre a lot lately myself and havent really experienced any issues with her 4 like that, so unless im misunderstanding theres no issue, just be mindful of when youre casting it