My first immediate thought, is adjustment period. You’re only talking a couple of days, and a lot of people have had various issues their first few days. Personally I didn’t… but others have.
I think so much of how Soylent impacts someone, is personal. Personal biochemistry, physiology, hell even psychology. I would say when you do try it again, to start out slowly. I’m not sure from this post if you went cold-turkey 100% Soylent or not, but personally I’ve always thought that’s a really bad idea for a variety of reasons. I tend to suggest people start out replacing just a single meal per day (or adding a meal of Soylent, if they normally skip say breakfast for example). Then gradually add a second meal if desired, and even go 100% over time if one really wants to (I didn’t). But zero to Soylent-only just really is a hard transition for the body, IMO.
As for the texture… I have not noticed the grit like you describe since letting the batch soak overnight before adding the oil. Don’t know what approach you’re taking, but I find this works amazingly well. From time to time I do feel like I need a swig of water after Soylent, but it’s definitely in the minority.
Hope this helps!