My rings are all on rotor spiders which standard shimano grx rings don’t fit.
You might be able to use a grx spider and fit a road big ring since you need the smaller bcd for 32/31/30.
The rotor grx compatible rings are only sold together which is a bummer. If I was to rebuild it, I’d go 50/31 just because sometimes the jump can be more torque than I momentarily want.
Thanks! I’ll check this out!
11speed DA Di2 here, with a working 52/34 setup (11-32 in the rear). Two tricks helped me:
a) The front derailleur’s lateral (in-out) adjustment (others already mentioned this). Pivotal for getting the front shifting to work, even with the “approved” Shimano 11-30.
b) Adjusting the b screw of the rear derailleur. Just a few hairs from the upper pulley touching the rear cassette’s cog, but no more. And it works beautifully with the non-approved SRAM Red 11-32T.
No power shifts, but then again I anticipate gear changes and 11sp Di2 makes it really easy to shift while braking.
Yeah… I was going to say something along the lines of “52/34 is not the intended pairing, but that shouldn’t cause shifting this poor”.
I’d definitely double check the adjustment settings.
Since it’s 12-speed DA, you can do this using the mobile app (maintenance tab), and write down the values for each of the steps before you change them. That way you can always go back to the previous value if the new one doesn’t work out 
No experience with this set up. There is however a setting in the Di2 app to set the chainring and cassette combinations on the bike.
is it possible that changing these settings might improve shifting? Just a thought.
Don’t wait for an Ultegra 11/36. Just use the 105 version and put all of this behind you.
Interesting! Curious, why do you think tightening up the B screw would help front shifting?
This set up will never work properly. Shimano road derailleurs are only intended to shift a difference of 16t. The di2 system needs to be told what rings and cogs you have to perform correctly and you cannot select out of spec options. The major issue is the chainring ramping is designed for proper ring pairs and nothing will line up if you mix and match. Everyone saying it will work has sub optimal shifting. It might work for you but you can not expect it to ever work perfectly or without quirks.
Apologies for not being clear…I had to REDUCE chain tension via the b screw, otherwise the chain was getting in a quasi state and not shifting to the big ring. Thus, chain length also matters.
I hear and respect what lucas_gallagher is saying about derailleur capacity. If I may add: Shimano’s stated capacity is very conservative. On my 10speed DA setup, I have been running an 11-32 in the rear, which is 4t beyond Shimano’s stated capacity, since 2010. Works like a well-adjusted Swiss watch.
I am not saying my 52/34 setup works like a Swiss watch, but it is very dependable, no dropped chains or delays. A low range of 1.06 coupled with the tall gearing of the 52T is awesome on the mountain roads and 15%+ inclines I experience. With your 34T in the back, the 1.00 gearing should be awesome even for centuries with 15,000+ feet of elevation gain (Triple Bypass, CO Death Ride, etc).
I didn’t read the full thread, but if not mistaken nobody yet brought in the idea of 51/34 gearing.
I was running that for ca 3yrs, i.e. 51/34 and 11-30 cassette Shimano mechanical setup, before moving to 1x SRAM setup on the road. Idea was also to have a broad gearing capacity but hesitated to go 52/34, and it worked very fine. Not perfect front shifting, but I blame the non-Shimano chainrings for that, rather than the chainring size difference. IIRC I was running Specialites TA chainrings.