Hello @Rezard 

Thank you very much also for providing the links, yes, we can see that there are different cases about issues with the Bluetooth adapter card, while some similar case are solved by trying different troubleshooting steps or replacing a hardware component that was proved to be defective, none of them are considered by TP-Link as a known issue with the UB500 adapter.  Can you help confirm some case details here to help fix the issue:

1.   For 'but if you turn off the device, after turning it back on, fails to reconnect.'

May I know how did you turn off the device, does the problem occur after you manually turn Bluetooth off or reboot PC?

2.  Please share a photo of the error message.

When problem occurs, please check if the Bluetooth's hardware is still recognized by PC as Q2 here 

Q2: What if my PC can’t recognize Bluetooth USB Adapter when I plug it in? (There is no Bluetooth Radios symbol in Device Manager)

3. What models of the Bluetooth devices? 

4. Please share a photo of the driver date and motherboard information as well

Kindly note we could help replace the unit under device warranty is a device is diagnosed as faulty,  while TP-Link does not have refund service (refer to local RMA policy here), if you prefer to get a refund, please reach the retailer to check the return window first. Thank you in advance for helping confirm case details.