In the other thread I noted that Flexi has indeed changed the RIP engine in major version changes but I do not think that is related to this issue... if that were the case there would be quite a number of users posting here all having the same problem and v22 has been out for some time now.
That being said I've also encountered things in Flexi before like a masked vector shadow with transparency (in other words a fairly complex object also mixed in with lots of other complex objects) when viewed in Design, selected then sent to Production Manager and when you pull the preview in PM the shadow is missing (and will not be in the print). Rarely happens but annoying if something like that does occur. Have also seen contour cuts doubled when copy/pasting before and with v21 I did see a couple of times where a stroke color would change.
It could very well be the RIP engine itself but it seems unlikely as the RIP engine is more what produces the final output in PM unless the RIP engine is also used in Designer to interpret, bring files in, and manipulate them in Designer.