For tricky problems you can add an app to record your user’s sessions, to try and figure out the problem.
Session Recording & Replay is a free app in the Shopify app store that can record your users sessions.
If you could set this up we can look into what the user is doing to create these bugs, or what device and browser the user is using.
Email us back when you come across a session recording with an error you want us to see.