At low FPS particle systems with "Previous Tangent Recalculation" enabled in the Ribbon Data result in messy mesh generation.
Found in 4.21 CL# 4753647, 4.22 CL# 6574378, 4.23 CL# 6925347, and 4.24 CL# 7062268
At low FPS, previous tangent recalculation causes incorrect mesh generation. At low FPS, particle ribbons with Initial Size followed by Size by Life reach unpredictable sizes. The lower the FPS at moment of activation, the larger the particles become that spawn now or in the future.
Previous tangent recalc should not generate messy meshes at low FPS. Particle ribbons with Initial Size followed by Size by Life should not result in different sizes depending on FPS at moment of activation. When Size by Life ultimately reaches 100%, the resulting particles should ultimately reach the same size as an equivalent particle system with only Initial Size.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-76434 in the post.