When did it stopped working? A few months ago?
I can check if something happens with this export mode in Blender. Otherwise, it is maybe that cinema 4D doesn't like collada with multiple materials assigned.

It's been about a month, maybe two.

@Superdooperhero, see this thread: https://www.mecabricks.com/en/forum/topic/280/1

If it helps. Anything with image maps come through mapped fine. Stuff with just simple colours don't. Also it doesn't make a difference whether you group by colour or not.

On my stunt copter the two slope bricks with a single colour comes through mapped, but all the other single colour blocks don't.

Read the thread referenced above thoroughly, export to .obj and use the script under https://github.com/mredig/Parse-MTL-C4D to import the materials (i.e. colours) exported to the .mtl file. That worked fine here. The grouping colours switch doesn't matter.

Note, that this won't provide you with accurate Lego shaders for C4D. You'll have to create your own C4D material library for that (unless you have Cycles 4D). Hence it's recommended here to use Blender for best results.

I did read the thread, but obj sucks compared to collada. So first prize is to get collada to work.

For me the OBJ format was the only way to get my models into C4D. The Collada importer is obviously not well supported by Maxon. Meanwhile i switched to Blender for MB stuff, because I instantly get good results.

I imported a scene via Collada into Blender, but it also looses the colours in Blender. I see Cinema 4D also support Collada 1.5, not sure whether that will help.

Hello,
It doesn't really loose colors. It is just that materials have to be set up correctly. This is the purpose of the addons I created.

Where can I find information about these addons?

This is all available in the shop section: https://www.mecabricks.com/en/shop
90% of the renders you see on Mecabricks use one of them.

Btw, C4D R20 comes with a new material nodes feature, see https://www.youtube.com/watch?v=MI_IS_Vpro4
With some diligence it might be possible to create a Lego C4D material library based on the MB Blender materials, so this would avoid the need to purchase Cycles 4D (IMHO Insydium should have made this free, since this is based upon open source code from the Blender devs team. But conceded, their team can't exist on love and air alone...).

But with Blender 2.8 coming out soon and Jacques Lucke (the maker of Animation Nodes, the "Mograph for Blender") now being on board, there's probably no need to use C4D anymore. Jacques will be working on the "everything nodes" project, so Blender is going to become kind of Houdini. Seeing all that development, I believe Blender has a really bright future ahead of it.

Some time ago Andrew Price did an interview with Ton Roosendaal: https://www.youtube.com/watch?v=qJEWOTZnFeg - a must see, for those who haven't yet!