Glaives currently have 2 major bugs that make them almost unusable. I have not seen anyone else reporting the first heavy attack bug, but I have seen numerous reports about the bugs while dual wielding.
The first bug occurs only with either quick return or volatile quick return equipped. Heavy attack detonations work as expected while the glaive is travelling away from you, but after impacting a surface or enemy heavy attack detonations will not deal damage at the glaive's location, despite the explosion visuals appearing as normal. The heavy attack detonation is instead triggered at the point the glaive initially impacted to trigger its return, dealing full damage and applying all other effects despite there being no visual indicators this is what is happening.
The second bug occurs when dual wielding a glaive with any secondary. If a charged or partially charged glaive is thrown, the heavy attack input fizzles and will not detonate the glaive in midair unless the input is pressed a second time during the same throw. In addition, any secondary weapons with alternate fire inputs (including incarnon weapons) will be completely unable to activate their alternate firing mode. There is no resolution for this bug besides unequipping the glaive entirely.
I have also included a video showcasing both of these bugs which I hope can provide a clearer example of what is happening, especially regarding the heavy attack detonation bug.
These bugs have a 100% reproduction rate at the time of posting and affect all glaives.