Prompted by a post in this forum I installed Emby on a clean Orange Pi Zero - it installs Mono v 184.108.40.206
An install from a few weeks back on a Banana Pi M1 pulled in Mono 4.8.1
I understand from the Emby forum https://emby.media/community/index.php?/topic/52758-odroid-xu4-frequent-crashes/ that Emby only supports Mono up to version 4.8.1 so any new installs will potentially fail. Something must have changed in the install script recently?
On my XU4 I have locked Mono to 4.8.1 by adding
deb http://download.mono-project.com/repo/debian wheezy/snapshots/220.127.116.11 main