@brolly759 said

I tried the above and it worked, if you have the time, try it to and let me know how it goes! :)

Well, perhaps you can backup your uboot, but it seems that you can't write it back this way:

# mtd write u-boot.bin mtd0 Could not open mtd device: mtd0 Can't open device for writing!

[edit]
You can, but it's not as trivial, so it requires some hoop jumping to get it done.

# mtd write u-boot-env.bin u-boot-env Unlocking u-boot-env ... Writing from u-boot-env.bin to u-boot-env ... # mtd write u-boot.bin u-boot Unlocking u-boot ... Writing from u-boot.bin to u-boot ...

[/edit]

I found that reproducable when i got error message for not enough disk space left. ... afterwards i saw such errors...start from zero. Restore factory default and do sysbackup with nee binary... Pain in the a... but thats the only way that worked for me..

@Matthew-Lousteau If @Maximilian-Gerhardt 's advice doesn't work, can you shoot a video of the behaviour? That will help us identify what's going wrong and how we can fix it.