I have used a Xante Impressia for a while now. Since you have already replaced the feed rollers it kinda rules out that option. Although depending on workflow may require more frequent replacement. The problem is most likely in the envelope itself. If you load to much in the tray it will most create to much pressure for the rollers to grab it. The flap is often a variable. It really depends on what exactly your doing. If the flap has sharp corners sometimes that can catch. I typically run flap face up towards the back opposite of the machine, unless I need to print on the flap itself. If it is actually feeding and jams in the middle, it could be your fuser. If you pull the fuser out on the right side there is a metal buckle adjustment to switch from a envelope to flat prints, You can try that. It's also just a xante which to be honest is just a glorified desk printer that can print envelopes. It has very little forgiveness and is typically a pain. Riso has better options for envelope printing. Just troubleshoot with it, change feed direction, does it print anything flat? Change the fuser buckle adjustment? Try a different envelope is that better? Is your size right? Try to just restart it. Eventually you will find the cause.
