Same exact problem. XPS 15 9570
This is not some broken-machine warranty issue. There is a defect somewhere (BIOS or Driver) that needs to be repaired. Dell -- please treat this with higher priority and look into it. I purchased the machine for my girlfriend and having her run through the BIOS or anything highly technical like that every time this happens is beyond her understanding and is not acceptable.
Same. I also have a Logitech MX Master mouse and and K780 Keyboard. It regularly forgets one or the other or both and the device has to be re-linked. The BT toggle also disappears so can't turn it off/back on. Also, the Bluetooth Devices screen shows connections (paired) for both the keyboard and mouse even though they are not connected. When I try to delete those connections it says "removing" and then says "remove failed". Instead I connect each device again and a second connection icon appears for each device. For each device, one says paired and the other says connected. Eventually, usually after the PC sleeps, the second connection will stop working and need to be deleted and reconnected. Just once (today) the second connection would not delete and I ended up with a third connection showing for my MX Master mouse. (Yeah, sorry. I know. Very confusing).
Glad to know that the problem is widely known. Same for me, MX2 mouse,latest dell 9575. Removing "dead" mouse works,but only for one of two positions. The second one always ends up with "remove failed" message. Dear Dell, please fix that.