Running into an odd issue. We have been deploying SL3 since they were released and been using the original Surface Dock. We recently placed a new order of SL3 and on connection, in no combination could I get our Dell monitors (miniDP to DP) to work. Hooked up the same SL3 with the new Dock 2 via USB-C to DP. They work. We are a pretty small firm but we have at least a dozen SL3 from earlier this year working on the original dock. I found this post (Surface Book 3 with Surface Docking generation 1 - Microsoft Tech Community) which the OP mentions the same issue I was experiencing. No matter the combination of original docks and cables (even ones that I have tested with prior SL3) will work. Using one external monitor, I could only get 640x480. Connecting two monitors, neither would work.
Not sure if anyone else can confirm this but this seems like something Microsoft should have addressed. I haven't seen any mention of a minor SL3 refresh this year. Would be curious if anyone can confirm this as well.