Yes, done all the tricks.

Clean all the contacts, new battery, etc. For some reason, it only happens after sitting for a few hours. Unscrew the cap, tighten it, & it works, for a short time.

It’s a known bug on the MR-50 & MR-70, documented here many times. Almost as many times as Rofis lack of customer service. I have just accepted I have a pair of over priced non-turbo flashlights. That’s why when leave home, I grab my Nitecore or Olight.