I’ve been trying to access a zynthian for m a raspbian Pi 2B and It is remarkably ineffective. Nothing seems to work in the basic menu.
They were superseded 5 years ago by the pi 3… Maybe try upgrading?
I just removed a Pi 2 from a 1 meter long image drawing wand project, to make it a basic voice box for an old keyboard. I should at least be able to confirm you symtoms in the near future.
Have you considered starting with an early Zynthian system archive as a last resort?
What is installed on the RPi2? What OS? What browser? What is the network connection?