Plugin logs out with no reason, re-login didn’t work

I use simplybook for two month now and I also installed the wordpress plugin for our website. During that time, it happend 3 times, that I got – for whatever reason – logged out of the plugin. I only noticed it, because some of our customers couldn’t book any more on our website. The last time, I had also problems to login again, because the confirmation code didn’t arrive via email. The simplybook support tends to claim that there is a problem on my side which isn’t the case. In the end, I don’t use this plugin any more, because I want to avoid bad surprises, when customers can’t book any more. For a premium account I would expect a more reliable solution and a better support from the provider.