There have been 3 reports from Japanese players on the official forum. 2 are now in "Unable to Verify" section, the third is still in "Accepted Bugs".
From my personal testing :
The nerf/glitch only affects magical Blood Pacts and is rather strong depending on the BP.
Before the update
Somnolence Vs Wild Rabbit : 3057 damage
Nether Blast Vs Wild Rabbit : 5267 damage
After the update (with the same equipment)
Somnolence Vs Wild Rabbit : 1721 damage (43,7% dmg decrease)
Nether Blast Vs Wild Rabbit : 3971 damage (24,6% dmg decrease)
The "Blood Pact damage" job point category doesn't seems to be the cause, although it was the only SMN thing patched on this update.
Lv 99 SMN with 0/10 JP on Blood Pact damage
Nether Blast 757
Somnolence 303
Night Terror 1104
Impact 1366
Wind Blade 1254
Lv 99 SMN with 1/10 JP on Blood Pact damage
Nether Blast 762 (+4)
Somnolence 307 (+4)
Night Terror 1108 (+4)
Impact 1371 (+5)
Wind Blade 1258 (+4)
Avatar/Spirit Mag. Damage has 0 effect on our BPs also (is it normal? was it always the case?) but I don't think it can be the sole reason to explain a so big drop in damage.