TPMS orange arning lights - sensor fault?

So on the motorway last night and got the yellow warning triangle, with the tyre icon. Reads "-- --" for the two tyre pressures. Pull onto hard shoulder, inspect tyres, fine, no issues. Cycle engine, ride off, no warning light; comes back after about 20 minutes and stays on so I ride through it and does same on journey home.

Have previously changed the battery on my TPMS sensors using the "glue gun" method to reseal it; mixed success. One of them appeared to work (give a reading) for a few months, the other didn't really work after battery changed at all. So I have had a read out of "-- --" on my TPMS for quite a while, but it never triggers the warning lights. So, why would it now start triggering warning lights? I assume this is an MOT fail under the new rules, so annoying and also dis-concerting (I felt nervous riding at motorway speeds on a long journey with a warning light, even though I knew the tyres were fine, but I didn't have a pressure gauge with me so couldn't be "certain").

So is this the bike saying "look, I've lost all communication with the TPMS sensors so you should do something about it" or is this the bike saying "I think your tyres are flat" ?? Is it more likely to be a fault with the bike's "receiver" or the TPMS "senders"? I see on motorworks they're £131 each so I'd rather not have to buy new ones if there's any way around it. Any wisdom appreciated. For example, is it possible for them to become "de-synchronised" over time and just need re-coding, or is that not really a thing?

Mine did something similar awhile ago and I had read somewhere deflate the tyre a fair bit and reinflate past required PSI and deflate to required PSI and it sorted my issue. .
Worth a try and nothing to lose .
Hope it works .
Cheers

Thank you for your reply. May I ask had your TPMS readouts been "-- --" for some time before hand?

Yep off and on for a while and cleared after I did the above procedure

Thanks, I'll give it a try.

I would fit a pair of the cheap sensors from Aliexpress they are identical to the BMW ones, The sensors I have had even have BMW on them.
I have changed the batteries in the past but with these being so cheap from China it is not worth the effort.
Plenty of threads on here about them you may need the £6 wake up tool to get the codes.

Mine have been doing this for several years. Front tyre I never get a reading, rear tyre get a reading for about 30 miles then the yellow triangle and ‘—.—‘ comes up until I switch off the engine then the sequence repeats. I know the TPMS is fucked so I just ignore it and manually check the tyre pressures weekly.