I understand that for a light roast (cupping roast to perhaps city +) you need to allow a bit more time for the whole bean to develop. When I go too fast there are distinct grassy flavours. On the other hand I had a few espresso batches that I roasted to City+ or FC (but definitely no 2C). They came out baked - a boring cup with little to no acidity despite a low final BT. My conclusion was that (even though the roast never stalled) there was a need for a certain minimum RoR to avoid baking.

After those batches I increased my RoR and all was good. I also changed other parameters though (like drop in temp and time spent in drying phase). Perhaps I made the wrong conclusion thinking that the RoR was to blame?

Do you increase RoR once 1C is finished?

That's not very descriptive, but IMO yes, you came to the wrong conclusion. I doubt holding a certain temperature for 2-3 minutes (as opposed to a steady climb) would result in baked flavors by itself.