LYWSD03MMC - can't connect after enabling "LE Long Range" even with BT5 USB adapter

[Tim]

I use a half dozen Xiaomi LYWSD03MMC temperature sensors with Home Assistant, they work well. I have an XDO bluetooth 5.0 adapter, which I usually have connected to a Raspberry Pi 4, but also works on my Ubuntu PC.

As an experiment to see if I could get longer range I disabled "BT5+ PHY" and enabled "LE Long Range" on one of my thermometers. I can't connect to that thermometer any more, either with the XDO BT5 adapter, with a modern Samsung phone that also supports BT5, or with a Google Pixel 4a that also supports Bluetooth 5 LE.

The sensors are cheap enough that they can be replaced easily, but I'd like to see if I can get it working again. I'm not interested in cutting up a USB cable and soldering to get a physical serial interface though. Can anyone help? Or have I ticked options in a way that mean it's basically bricked?

Here's the details of my Bluetooth adapter

hciconfig -a
hci0:	Type: Primary  Bus: USB
	BD Address: 00:E0:42:8B:xx:xx  ACL MTU: 1021:6  SCO MTU: 255:12
	UP RUNNING PSCAN ISCAN 
	RX bytes:5737 acl:0 sco:0 events:341 errors:0
	TX bytes:32992 acl:0 sco:0 commands:303 errors:0
	Features: 0xff 0xff 0xff 0xfe 0xdb 0xfd 0x7b 0x87
	Packet type: DM1 DM3 DM5 DH1 DH3 DH5 HV1 HV2 HV3 
	Link policy: RSWITCH HOLD SNIFF PARK 
	Link mode: PERIPHERAL ACCEPT 
	Name: 'RTK_BT_5.0'
	Class: 0x000000
	Service Classes: Unspecified
	Device Class: Miscellaneous, 
	HCI Version: 5.1 (0xa)  Revision: 0xdfc6
	LMP Version: 5.1 (0xa)  Subversion: 0xd922
	Manufacturer: Realtek Semiconductor Corporation (93)