Spool jumping on Brother Machines (no spool caps)

I have a Brother XM2701, which isn’t supposed to require a spool cap. When I first got it I noticed the top spool jumping around and winding unevenly. At first it seemed to be some spools but not others (typically using Coats & Clark Dual Duty). Literally picking another color threading it seemingly the same fixed it. Over time it’s become all spools. My husband just got a Brother LX3817 and threaded it with the instructions in front of him too (multiple times). It will do well for a few stitches, jerk and create slack, sew okay until it uses its slack, repeat. The result is of course it’s hard to get consistent tension. I’ve got a thread stand coming because I’ve seen that as advice, but was hoping those of you who have been doing this forever (or had the issue and solved it) could lend some advice, since those seem to be more for the cones so I’m not sure it’ll work. Is there an after market thread cap these machines can use if the thread holder doesn’t work or is this type of thread known for this/not machine compatible? Should we be leaving some slack when threading the top (instructions don’t address it, but we’re following every thing else in them to a “T”)?