Stomach issues on unflavoured but not with vanilla

Finished my first bag of vanilla Huel with a small uncomfortable adjustment period, but nothing too major.
Had two scoops left, so added a single scoop of the unflavoured version. I felt a bit weird after. Following day I continued, now with 3 scoops of the unflavoured… resulting in a very unpleasant evening.

Does this sound familiar to anyone?
If so, did things settle down?

I’ll definitely continue with vanilla, but not sure it’s worth the risk with the unflavoured one - my stomach reaction was pretty severe.