The problem is missing updates for TS12 built-in assets:
Unknown Location: <kuid2:30671:9252101:2>
Earlier version: Limestone aggregate by llj, <kuid2:30671:9252101:1>
Unknown Location: <kuid2:330374:1024:40>
Earlier version: Sig AS UQ 15ft home semaphore RH by francelinetony, <kuid:330374:1024>
Unknown Location: <kuid2:60850:23151:3>
Earlier version: UK rail buffer stop (lit) by bloodnok, <kuid:60850:23151>
Unknown Location: <kuid2:67794:28005:8>
Earlier version: CementProcessingPlantV2 by fitz505, <kuid2:67794:28005:2>
My suggestion: Either push the original content owners to post their updated content on the DLS, or create a new version of the route (rtclk->Create new version) and update the KUIDs with the versions that are built-in TS12, then commit and upload.
EDIT: Same story with the session.
Unknown Location: <kuid2:30671:9040500:2>
Earlier version: Butter, pallet by llj, <kuid2:30671:9040500:1>
Unknown Location: <kuid2:30671:9040690:2>
Earlier version: Cheese, pallet by llj, <kuid2:30671:9040690:1>
Unknown Location: <kuid2:30671:9252101:2>
Earlier version: Limestone aggregate by llj, <kuid2:30671:9252101:1>
Unknown Location: <kuid2:44090:10000:2>
Earlier version: BR BD Container by paulhobbs, <kuid2:44090:10000:1>
Unknown Location: <kuid2:44090:10001:2>
Earlier version: BR FM Container by paulhobbs, <kuid2:44090:10001:1>
Unknown Location: <kuid2:44090:15077:40>
Earlier version: BR Conflat A Diag 1/061 by paulhobbs, <kuid2:44090:15077:4>
EDIT2: These assets you want us to use are built-in for older versions of Trainz, but not for TS12 alone. This was confirmed by looking at a copy of TS12 that has the ja files for TS2010, TS2009, and SnC. My suggestion is to do all your route edits on a clean install of TS12. That will ensure that all your content is either built-in for TS12 or on the TS12 DLS.