It's the way kernel update come in apt. The kernel update is a new package, not an upgrade of a previous kernel package. Thus the old kernels are left in place and the new ones installed alongside. After about 3 kernels have been made available in /boot the previously recommended size for /boot is full and attempted update to a new kernel fails.
It can be manually fixed by removing older kernels ("sudo apt purge ...").
Perhaps I'm mistaken but i thought a fix was in place for this, maybe it was something third-party but apt definitely offered to remove unused kernel package for me recently.
What? This is ridiculous and unacceptable. I don't use Ubuntu anymore, can someone tell me what is filling up the boot partition?
I'm currently on ArchLinux and mine is 200MB and it's 14% full! I can't fathom what could occupy so much space.