Can't bind T16 (default 4-in-1 transmitter) to EU LBT FrSky XSR or R-XSR recievers

Hey - I’ve upgraded from a Taranis X7 to a T16 from UMTS and I can’t bind the T16 to either my XSR (in a big drone running Arducopter) or R-XSR (in a mid-sized drone running Betaflight).

I’ve followed the instructions carefully (put T16 in bind mode, quickly power reciever on with bind button down). Both red and green LEDs come on solid. On the T16, I’m using the “external” bay in the menu, which is the supplied Jumper 4-in-1 JR module. I’ve tried changing the receiver number several times just in case. I’m using Mode: MULTI, FrSky, D16.

I have successfully had the X7 bound to both receivers in the recent past (verified the R-XSR a few mins ago) - so the recievers are good.

I’ve updated the T16 to the latest firmware and SD card contents - the version shows as JumperTX-t16-2.2.3 (f568d3dd) 2019-07-26 05:53:59. I’ve updated the 4-in-1 module to the latest version I could find on Jumper’s site, Multi-STM_TXFLASH_INV_OPENTX-v1.2.1.69.bin, and in the menu near bind it reports the Module status as v1.2.1.69 (it was an earlier version prior to this update).
The Taranis is Opentx 2.2.4 (66bb9c3a) 2019-07-11.

I’ve flashed the firmware on both receivers in the past and I’m pretty sure it was to the EU LBT variants, but am unsure how to verify this (sadly the download files contain both variants and the one on the bin file I copied to the Taranis has been nuked).

I believe the problem is conflicting EU/non-EU firmware - but I can’t see a way to flash the 4-in-1 to anything other than one version with no EU/non-EU variants. I’ve also seen someone saying that the LBT bit isn’t properly implemented (doesn’t "L"isten first) by Jumper but should work.

So - I’m a bit puzzled as to what to do next - any suggestions would be welcome.