I’ve had the same issue with my Kegberry installation and in my case it was also an issue with sending e-mails. I had configured GMAIL as described in my installation write-up but was having problems when I started a pour that created a new Session. I have my e-mail settings configured to send a mail when a new sessions starts, so that initial pour would fail to register. If I manually created a new drink, the email would usually go through and then every pour after that would work perfectly since it was not trying to send a message.
The issues with mail configuration, including GMAIL are documented HERE and HERE and I believe I was running into one of these exact scenarios.
Because of this I have switched over to using SparkPost as my automated e-mail service and it has been 100% successful over the past couple weeks. The SparkPost service is 100% free (750 messages per day, 15,000 per month limits) but does require you to have a domain that you control and can manage DNS settings which usually has a cost. I’m using Google Domains which is $12/year per hostname.
I’m happy to do a reply post to my Kegberry New Installation thread with instructions for setting up and configuring the SparkPost service if this would be of interest.