Metallic threads and all others that are giving you problems: slow down the machine. I often do that when I'm test stitching too, as it's easier to see what happens than when the machine is going full speed.

Slow down the machine for stitching Free Standing Lace Designs.
Also when using metallic thread for designs.

Depending on the top speed of your machine you may just want to slow it down abit for any embroidery.
I think this helps the stitches form better and cuts down on thread problems.
Not top speed and not the slowest speed!

EastWitch2

don't forget also on heavier fabric too.

As the others have said, with FSL, metalic threads, I also often put it on slow if I am doing a very small fonts. I don't think there is a general rule, except for FSL. - Hugs Yvonne

When I'm doing denim or thick heavy fabric I will slow the speed down.

My machines are capable of 1000 stitches per minute but I don't do the maximam speed. My multi-needle stays on the default seeting of 600 SPM. My Ellisimo is at about medium to slightly higher. I would prefer to be a little slower than have problems.

Only if it is raining ;)or you are doing FSL or metallics.;)