This does fix a bug, but not one that needed fixing. Seraph could sometimes act too quickly, causing her abilities to not appear in the combat log (or floating combat text).
Here is a gif of it happening. What you're looking for is my HP going from 8160 to 13362 (+5202 HP), and me gaining a shield buff as Seraph is coming out. No floating combat texts shows any healing on me, nor does the combat log. I even get another passive health regen tick before Seraph casts a Seraphic Veil on me for 5256 that does appear in the log.
This is what the combat log looks like for this time period:
[14:41]Eos casts Embrace.
[14:41] You recover 55 HP.
[14:41]You use Summon Seraph.
[14:41]You use Consolation.
[14:41]Critical! You hit the striking dummy for 246 damage.
[14:41]Seraph casts Seraphic Veil.
[14:41] You recover 5256 HP.
[14:41] You gain the effect of Seraphic Veil.
The important distinction is that even though this was technically a bug, it didn't impact gameplay at all. The heal still happened. Putting a 2-second "summoning sickness" on Seraph just seems like a cover-up for game engine/server deficiencies.