Version 12.10.0+git20151221-5 of appindicator3-sharp is marked for autoremoval from testing on Mon 25 Mar 2019. It depends (transitively) on gtk-sharp3, affected by #921785. You should try to prevent the removal by fixing these RC bugs.
Last update: 2019-02-20
Standards version of the package is outdated.
The package is severely out of date with respect to the Debian Policy.The package should be updated to follow the last version of Debian Policy
(Standards-Version 4.3.0 instead of