I submitted a bug report about this, but I wanted to see if perhaps I had missed something in previous release notes that indicated that this was a known issue, or WAI, or anything like that. Plus, we all know the current bug reporting system does really, well, work in any way shape or form (Glad to see that's being addressed this year!)
The bard spellsinger T2 ability "spellsong vigor" slowly restores SP to a target over a duration of a few minutes, depending on the bard level and enhancements.
The item "vile blasphemy" obtained from the abbot raid also restores SP when used, at a slightly higher rate but for a longer duration.
Prior to U17 there was no issue using a vile blasphemy while spellsong vigor was active, and bother regens would stack. That appears to have been broken recently, and I'm not sure what change might have caused this.
If spellsong vigor is active on you and you try to use a charge of vile blasphemy, it will use the charge but not apply the effect. Additionally, if you use your vile blasphemy and then have spellsong vigor applied to you while the effect is ongoing, the vigor will remove the regen effect from the vile blasphemy.