Ulcerative Colitis flare from flu shot?

I’ve had UC for 3 years and finally reached remission for 13 months on Entyvio infusions. All other treatments had failed (oral and rectal mesalamine, oral and rectal budesonide. Oral prednisone was an effective bridge while transitioning to Entyvio. Remission started shortly after the loading doses. Also started a plant based diet at that time. I was doing great- even annual colonoscopy showed significant mucosal lining healing! Life was good and I was optimistic and hopeful for the first time in a long time (far cry from “fulminant” diagnosis in June 2019. Last Friday I had my annual flu shot and within 24 hours, I’m in a bloody flare after 13 months of remission!!! Nothing else has changed! GI doc has ordered blood and stool labs and I am devastated to be back in this all too familiar hell. I’ve read that there have been cases of people with UC flaring after getting a flu shot. I had never heard that and right now I just need some advice, support, hope.... Anyone ever had this experience??? Thanks!