Rifter Immobiliser fault. Not starting

[Cymboline]

I have a 2020 1.5 bluehdi 130 gt line Automatic. It wont start and displayed "electronic immobiliser fault". I put new batteries in the key fobs and checked the main car battery. It has now gone into eco mode and just displays the 3 warning symbols for parking brake fault and a beep when pressing stop/start. No other dash lights come on.
Pressing the stop/start does nothing, the parking brake is on and nothing happens when pressing it off and it was stuck in gear but I have manually put it in neutral. It locks/ unlocks and the windows work using the fob. When leaving the 2nd key in the vehicle it wont lock from outside (as expected), which would indicate that the system does detect a key is present.
The car did go to a main dealer for a camshaft chain recall last week after a 3 month wait. They did a full health check, software update as well, which was all fine, and I have done 90 miles since in 6 trips.
Anyone any ideas. The main dealer cant look at it until July!!!!

[Sloppysod]

Have you re-initialised the remote to the car?

Sorry, can't help with the how, but it should be in the same section of your owners manual as fob battery replacement.
re-initialised your spare remote, as they go to sleep if not used for about 14-21 days.

[PaulC5]

I would have thought reinitialising the remote is only if it does not work the central locking and has nothing to do with the immobiliser. However, if your car is keyless opening and starting then it may be different. Eco mode will clear when the engine is running but it could be the main battery could do with a charge.

[Cymboline]

Ok Thanks guys I will have a look at re-initialising.

[wheeler]

When the fault occurs have you tried holding the remote against the emergency start pickup on the side of the steering column?
If you hold it here the car should start even if there is no batteries in the remotes

[Cymboline]

Update............ Thanks for your suggestions but nothing has worked. My local garage has got it out of eco-mode but said there is no communication from the bsi to ecu and have diagnosed it caput. They have ordered a new bsi coded to the car. Expensive part but hopefully will fix the problem. I'll post the result in 3 weeks when part arrives from Peugeot.