Some Performer skills haven't been working as intended based on the descriptions and the information from the websites. Specifically, Song of Siren, Gloomy Shyness and Harmonize.
Song of Siren has been mentioned in a previous post
Siren's Voice Bugged Duration - MuhRO Forum
Gloomy Shyness
Does not have a custom change based on the battlegrounds wiki - meaning it should be 20 second duration with 60 second cooldown. But currently it has 20 second duration and 15 second cooldown.
In terms of BG, especially since it's a low population - you can pretty much hold someone hostage and make them have a permanent uptime of +2.5 fct. And even if they @die, due to battlegrounds having a cooldown before you spawn, the moment you even spawn back, you just get gloomied again. Maybe increasing the cooldown to act similar to WoE (20 sec dur, and 20 sec cd) would be good.
Harmonize
Based on the Skill Description:

It should only remove the battleground buff that gives us +30 all stats, but in reality, it takes more than 30
Sample (Before and After)
Before Harmonize:

After Harmonize:

It is taking upwards to 72 of my stats (Agi went from +57 to -15) and not the flat 30 that is expected. Furthermore, this skill was supposed to be balanced as the caster would lose the same number of stats as well. But Maestro's can just perform a song that belongs to Group A (Windmill Rush, Echo Song) and this "detriment" is moot point, meanwhile the target is still running around with less stats than they should.
Additional Note is that this song has a 5 sec CD with a 15 sec duration, meaning you can just permanently harmonize someone (like gloomy) and up to 2 people with ease (potentially a 3rd person too)
Proposing that this song gets a special group so that no other Maestro songs can remove this debuff from themselves, or when they perform another Group A song, the debuff from the target also disappears.