Ceres - Ker; Enemies become invulnerable after attacking a prosecutor

[WarBoo]

When doing this mission (solo using Zephyr, Heliocor as Melee weapon ) it works OK until I meet a Prosecutor. I suddenly do no damage, cannot kill him and more enemies are spawning that cannot be killed. I then can only abort the mission. The behaviour is repeatable (reproducible). I have restarted the PC but it does not help. Cannot do this mission anymore with this configuration.

[UPDATE] Switched to another Warframe (Volt), having the same issue. Next, switched Heliocor for Tipido, and then had no issues. Can kill multiple Prosecutors. So it looks as if the Heliocor is causing the issue.

[UPDATE2] Have issues with other weapons as well. The prosecutors are almost invincible. Any enemy in close range also become almost invincible. Running away from the culprit (but it comes after you) far enough allows me to kill other enemies again.