I've got a Bkool Pro and I've never experienced this problem in races. I've only done one workout ride and all was fine with that too. Sometimes I find a lack of resistance at the start of a ride, but I'e always found switching the trainer off at the plug and back on again sorts this out. There's already been plenty of discussion about the fact that the watts shown by the Bkool aren't always accurate and are often over-generous, but apart from this it works fine, and definitely never had the problem you describe.I knew there were problems but Whorty suggested all is OK using a bkool trainer on Zwift.
It’s ok for a normal ride but for me it’s bugged on everything like workouts and races!