Intermittent Flashing ABS light with triangle 2001 NHW11

I've just put a new Toyota HV battery in the car and all is well on that front. The car had been standing for a few months.
Unfortunately, the ABS, PS, & triangle warning lights frequently come on at startup. This is accompanied by spongy but working-ok brakes. The PAS seems OK. Switching off and restarting after a few seconds usually clears the warnings, and the brakes go back to normal feel.
I have fitted a new 12v battery too, but no change.
No codes on Scanguage 2: jumping the TC & CG OBD terminals just gives a flashing ABS, doors open, and airbag warning lights with no discernible pattern. It also brings up a page in japanese on the Multifunction display, with OK shown in 3 places after a few seconds, also the number 340 and OK next to that.
I do have a TIS clone but can't get it installed on my laptop so I can't diagnose further until I get that sorted.
The brakes work fine; normally if the warnings are off, and just with a longer pedal needing more pressure if the warnings are on. I suspect a lazy booster pump, but I'm surprised there are no blink codes.
Any ideas anyone?

 

The problem just went away with regular use, but has recurred following lockdown.
Codes 1571 and 1572 ( vehicle speed sensor) on tech stream, everything else is apparently ok.
Not sure where to go next; is it just the abs sensors, or is there a separate VSS?
Not having a paper manual makes everything a bit difficult!
Any wisdom/ comments gratefully received.

 

The problem came back, and eventually I took it to a main dealer for diagnosis. They plugged it in, and found nothing wrong, no codes etc. However, it seems to have fixed itself after being connected to their computer, and suddenly it now goes much further on battery alone. They did say the drive battery was low, and if it’s below 60% then the warning light will come on. I hadn’t done anything to update since the new battery went in so I suspect a software update or reboot has sorted it out. Fingers crossed.