Tvheadend

Most likely the DSM upgrade wiped out your symlinks. Most of those types of hacks to get things working for (sort of) unsupported packages tend to not survive a reboot, let alone an OS upgrade.

Stop the Tvheadend service, recreate your links and ensure that the Tvheadend user can see the grabber in $PATH, then restart Tvheadend.

(Personally, the limiting nature of trying to get third-party apps to build, run and persist in Synology's limited Linux install was the reason I had to move to setting up Tvheadend on a small NUC-type of machine. Synology may publish an SDK, but it's definitely not user-friendly to figure out why your own custom packages won't work.)

Exactly right, the symlinks were lost in the upgrade, but I have already restored them - and need to create a script to do so in the future. You raise an interesting point though: can user sc-tvheadend-testing see the grabbers in $PATH. The TVH user used to be tvheadend-testing when it was working, but has now changed. How can I determine its $PATH? It is not listed in the DSM Users list.

One difference I notice is that the old user, tvheadend-testing is a member of the Users group, while the sc-tvheadend-testing is a member of the tvheadend-testing group. I think I might have added the Users group manually long ago, seeing that it shows up in DSM Users interface, but I can't remember specifically. Both users are NOLOGIN.

Looking at the installation script (/var/packages/tvheadend-testing/scripts/installer), the following lines seem to argue that the standard bin locations should be visible in the TVH path, the standard path having been concatenated in:

PACKAGE="tvheadend-testing"
INSTALL_DIR="/usr/local/${PACKAGE}"
PATH="${INSTALL_DIR}/bin:${PATH}"

Found and fixed an issue with placement and permissions of xmltv files after DSM upgrade. Grabbing is working now.