Vertex color is removed on the tycache

[tyFlow]

I'm guessing the Vertex Color modifier clears data if topology changes, similar to the UVW Unwrap modifier. Perhaps it evaluated on a frame where the tyCache data was empty, causing the reset. Assuming that's the case, I'd suggest doing the Vertex Color modifications on the input geometry of the original tyFlow, rather than after the fact on the tyCache. Either way, this isn't a tyFlow bug