Steps to reproduce:

1. Open attached project.
2. Open scene: REPRO
3. Press play.

Expected result: Two particles are small in size and looks nicely.
Actual result: Visible artifacts or particle glitch are visible on the left particle.

Notes: With other meshes does not happen. Does not happen with default meshes. It's not the only mesh that this happened.
Also, visual appearance changes slightly if color over lifetime is unticked.

Not reproducible with: 5.5.0b11, 5.6.0a6
Reproducible with 5.6.0b1, 5.6.0b3

Regression introduced somewhere between 5.6.0a6 (af2099d5a7ac) - 5.6.0b1 (d37b23d9dfff)