Tim wrote:
Hello.
Has anyone managed to solve this problem, or is the R2S a completely non-functional device?

I posted the solution.

https://cloud.mail.ru/public/gDju/LHymPALVd

try this, maybe your R2S can boot.
(R2S Plus now work again)

Same issue dude. New firmware brick my R2S plus
All other firmware like ubuntu can flash and boot, but all *wrt.img cant, even old versions don't work.