Rae from Shopify here. Thank you for reaching out to let us know about this situation. I'm sorry for the issues you're experiencing with the card reader disconnecting, and I would be glad to help troubleshoot this further with you.
Just to confirm, is this the card reader you're currently using?
Can you also please let me know which device the card reader is connected to?
I know you mentioned that you recently upgraded, but was this update done to the software on the device you're using, or to the POS app itself?
If you haven't already, please make sure to update the device you're using, as well as the POS app, as ensuring both of these are up to date can help the app - and the hardware connected to it - run smoother.
Once I hear back from you with more details about the card reader and the device you're using, I would be glad to help further with this.
Based on my experiences I'd always recommend manually checking the App Store to see if there are any pending updates for Shopify POS. Between that and the fairly regular Apple iOS updates that are released. It seems to fix issues like this more often than not. I've also had to disable all networking services on the iPad, remove all remembered Bluetooth devices, and then re-add them from scratch. That's always a Plan Z but can help :)