This is a problem that I would say (with confidence) that everyone who uses Square Contactless & Chip Reader encounters; most of us encounter it several times per day, every day. Square will always say that it is your tablet/phone, your OS version or your internet connection. My Wifi will enable a laptop to function flawlessly about 70ft away from the main tower and modem, but Square on my tablet 10ft away from those two things functions in a very hit and miss fashion. The CCR is 14 inches away from the tablet.
I've been with Square for 7 years and have had the Contactless reader since it was first issued and have had the issue of the reader unpairing itself several times a day right from the start. In that time, I have had three tablets (RCA, Asus, Samsung) all on the compatible list, all displaying the same problem with Square, while working faultlessly with every other application. My OS is up to date, my connection is insanely strong and the Square app updates itself. Every time, I have been told by Support that it is my tablet or connection and it is NEITHER. The problem lies with the reader itself, I am nearly certain.
Sometimes I can fix it by turning Bluetooth off and then back on, rather than going to settings>card readers>forget this reader and then pairing the reader again. Point here is that I should not have to do either of these things, especially not on a several times per day basis.
All that being said, I stay with Square because it means less paperwork for me and because I get my deposits quickly