You don't need to be an 'investor' to invest in Singletrack: 6 days left: 95% of target - Find out more
It’s a Di2 hydraulic brake which is behaving a bit, uh, weird with regard to lever return.
If you squeeze the lever gently to full travel and release, it takes about two seconds to return to the neutral position. It’s almost as if it’s damped.
Grab firmly and abruptly, and the lever snaps back as normal.
Brake performance is normal, just feels strange. Pressure isn’t maintained on the pistons while the lever is making its way back.
From a troubleshooting perspective, I’ve replaced the brake calliper and flushed the oil. Has anyone seen this problem before? It’s under warranty but I really don’t want to be without the bike for two months while it’s replaced by Canyon/Madison.
I've come across strange feeling road levers a few times, not quite the same symptoms you've got, but every one has come down to a little piece of black plastic blocking the insert in the hose inside the lever, may be worth a look.
I've got the exact same symptoms with my Di2 Ultegra hydraulic. It's been like that since the bike was new (also a Canyon, coincidence or pattern.?).
I have been meaning to strip out the hose as I had read the same as @coatesy said about blocked insert but to be honest it's not affecting the brake parformance, I don't notice the slow return when actually riding (in fact mine seems to 'loosen up' after a few firm pulls on the lever), so I haven't gotten around to it.
Update: I think I've identified the problem.
[img] 
[/img]
The grease used by Canyon when they assembled the bike has failed (or reacted with the mineral oil in the brake) and turned into a fragile rubber. It's a mess. It's like it's become a sort of cheap silicone sealant.
My guess is that some of the grease has entered the master cylinder during assembly and solidified, and is now blocking an oil port somewhere. This would also explain why it's affecting your bike too, H1ghland3r.
I spent an hour picking bits of shite out of the lever and flushed the master cylinder and hose in both directions but without success. Seems a little better but the proof is when the system gets hot.
Raised it with Canyon's warranty department. Cannot imagine they're going to be that helpful but hopefully more useful than Madison would have been if they received a brake lever full of rubber debris.
Edit: I also draw Your Honour's attention to the use of grease on a carbon bar. 😐
Lots of bikes come with that grey sealant, Shimano UK tech support say its used at the factory assembly (but only on some bikes?), but they dont sell it, and we dont need to use it because its not necessary?
I have had a few bikes in with it partially blocking the brake hose insert.
That's the standards hydraulic sealant fitted by Shimano. Failure of Shimano hydraulic STis is quite common - just get Canyon to sort you out a warranty replacement lever.