Ubuntu 18.04 LTS

Pre-installed in some regions with a custom Ubuntu image that takes advantage of the system's hardware features and may include additional software. Standard images of Ubuntu may not work well, or at all.

Upgrading bluez to 5.50 as mentioned in link below can fix the problem:

https://asksne.bianheman.eu.org/questions/1036195/bluetooth-doesnt-work-after-resuming-from-sleep-ubuntu-18-04-lts