Relation between CAN errors & IQAN Design 6?

The past year (since Februari or so), we've been experiencing a lot more CAN related issues than in previous years. Usually BUS-ERRORs (so the safety module will lock down). It happens sporadic, it has been extremely hard to reproduce, but it happens on quite a lot machines, a few times a week in some cases. Machines with different software, different engines (FPT, Scania), different programs, different wiring. So they must have something in common that makes this happen.

I suspect it's "just" somewhere in the wires/terminators or other external factors that may reduce the bus health in general. But, what strikes me it started to happen on somewhat older machines, after updates. Some MC4x modules went from IQAN 5.03 to IQAN 6.xx, and it seems that CAN problems started there as well.

Could it be that the problem was always there, but that IQANs have a more strict check (less tolerance) since a specific firmware version?

Couldn't find it in the release notes, other than that several new CAN features (high speed, FD) have been added. A bit off topic, but in the same fashion we just updated a very early MC43 with a new program, and suddenly there is a VREF error that didn't occur before the update. Again, I guess the error was always there, but slipped through somehow in the older firmware?

For the info:

* We use 250 kbps

* Faults happen on the primary CAN-bus (about 4 MC IQANS, a display, an Engine)

* Usually the Safety Module will lock down, while the others continue to talk

* Networks are often a mixture of firmware versions (IQAN 5.03, IQAN 6.00.49, and more recent IQAN versions) - depending which modules got updated