Both my character and Ifan could not heal from Blood sucker when casted on blood pools.
Do you (or whoever is hosting) have a save handy where this can be reproduced?
Please email supportdos2@larian.com, with a brief description and a save (or a Dropbox or Google drive link, etc). Each save is a folder in the '..\Documents\Larian Studios\Divinity Original Sin 2\PlayerProfiles\<ProfileName>\Savegames' folder. In Windows Explorer you can zip file(s) and folder(s) by right clicking on it/them and selecting 'Send To | Compressed (zipped) Folder'.