Sorry to hear it – that definitely shouldn’t happen!
I do notice you are a few (minor) versions behind, in relation to your copies of Event Tickets and Event Tickets Plus. Can you update those? Similarly, WooCommerce appears to be a little out of date.
Can you tell me a little more about your tickets – are they set to use shared capacity or does one/both have a fixed, non-shared capacity? You can check on this by editing each ticket – you should see something similar to this:

Thanks!