As well as Bloodvelds attacks seem to take into account the players melee defenses instead of magic defense.
for bloodvelds specifically, was able to tank them way better in full rune gear with -20 mage defense
with full black d'hide (+80 mage def ish) took way more frequent damage.
tested with multiple runs.
'09 wiki links of Cave slime & bloodvelds for reference:
https://runescape.wiki/w/Bloodveld?oldid=895705
https://runescape.wiki/w/Cave_slime?oldid=885380
Here the full list of mobs I've personally encountered with this Issue, but I assume this would be the case for almost every monster that is poisonous or has an unique attack type.
Zammorak gwd boss poison seems to work fine.
Poison:
- Cave Slime - ID: 1831
Kalphite Guardian - ID: 1155
Cave Crawler - ID: 1600
- Bloodveld - ID: 1618
[Moderation edit: Locking as NPC poison issue has been reported on gitlab several times and magical melee is unimplemented]