I am encountering a periscope bug with Ifrit/Hunter HMG/GMG variants similar to ticket 0017112.
Starting the missing inside the vehicle causes the issue.
Getting out of the vehicle and climbing back in resolves the issue.
Tried in latest Stable(1.18.124.200) and Dev build (1.19+) and encountered but in both.
Start Editor
Place Ifrit or Hunter HMG or GMG variant with Player As Gunner
Try to use weapon optic, if it works, restart Editor mission and try again, as sometimes it will work for me but after restarting the mission it would not.
To fix the bug while in the mission, exit and re-enter the vehicle, optics should work now.
Ticket 0017112 was opened due to similar bug occurring in helicopters but was resolved.
Just wanted to add that this bug is also affecting the scopes of static weapons as well in the latest Stable build. If you place a an HMG or GMG car or static weapons in the editor, after starting and restarting the same mission sevreal times you will eventually not be able to use the scopes of any car or vanilla static weapon.
Usually occurs after the third or fourth restart but sometimes right away. Tested with no mods running.