This sounds to me like a fuel pump issue. I have a WR250R (2012) fitted with the later pump, and it fails intermittently with exactly the same symptoms as your bike exhibited initially. Most of the time, the WR runs fine, which means no chance of warranty until it fails completely.

Pumps do fail gradually at times, and my 250 is like this. A Chinese pump is in stock here at home ready to be fitted. I bought a spare Tenere one too. Total cost: about $90AUD.

The Chinese ones come with a new in-tank filter, too.

Regardless of what your issue is, I hope you get it sorted soon.