Comment 4 for bug 1714504

The same is happening for me with the Synology Cloudstation Client and additionally, Cadence, the Jackd manager app. Also only happening under X and not Wayland.
This was actually working before Ubuntu got it's hands on it so it was a recent update. The version on Gnome Extensions I assume has had the same patches applied as it is not displaying icons now either.
It stopped working two updates ago.

Happens at log-in.

But to add a twist to the plot, I have the exact same behaviour with Ubuntu 17.04 running Unity 7! I would have missing app-icons under X but they would display fine under Wayland.

Yet still, with this current version of the problem, it only started happening in the past month.

Therefore, I put it to you that the issue is not so much with this package but potentially a patch in X that was recently applied. Probably the same patch they used in the previous version of Ubuntu at some point.

Likely to be an Ubuntu customisation of X rather than the appindicator package.