I have the latest Quicken Classic, version R58.9, build 27.1.58.9 on an up-to-date W10 system. I can get my desktop data to go to the mobile app if I choose Mobile & Web→Cloud Sync. If I use One Step Update→Sync to Quicken Cloud, the data doesn't transfer. This is true on my largest Quicken file. The smaller ones work OK.
Cloud Sync takes much longer to sync, so I'd prefer using One Step Update to do the syncing, where it also downloads prices, etc. with 1 click. To get everything done, I now have to do One Step Update then Cloud Sync, which is a pain.
I've tried Edit→Preferences→Mobile & Web→Reset your cloud data, to no avail. My accounts are selected for Mobile & Web properly.