I've seen three different issues that I haven't been able to consistently replicate, each has happened 3+ times on different machines. They all have the knack of showing up during training classes or Tableau office hours sessions, not when I'm able to really dive in to try to figure out what's going on.
1) Tableau Desktop for Windows versions 10.5 and 10.5.2 - somehow it loses track of built-in mapping capability. The Geographic Role field menu option is gone, maps don't show up, etc. The only workaround I've found is to totally reinstall Tableau. Never seen this on Tableau Desktop for Mac.
2) Tableau Desktop for Mac and Windows version 10.5.2 (and maybe others) - In dashboards sometimes the Fit options completely disappear from the worksheet carat menus. For this one quitting Tableau and restarting & reopening the workbook has worked.
3) Tableau Desktop for Mac and Windows versions 10.5.0 and 10.5.2 - Views using the native Excel & text file connector (i.e. using shadow Hyper extracts) and/or Hyper extracts occasionally throw "query failed" (not the actual text) errors when opening or refreshing views, refreshing the view again doesn't get the error the second time around.
There is one big issue I encountered in Tableau version 10.5: Append operation does not work properly with Data Source Filter. I am raising a ticket and will keep you posted.
We have been on Hyper for 2-3 weeks. It turns out as a smooth upgrade overall. The biggest issue we had was x-db joins among two or more Excel. Those Excel are loaded to Tableau server as part of the publishing process, not on shared driver. After 10.5 upgrade, the browser just spins and nothing comes back for those workbooks although the render time was seconds before upgrade on V10.4. The fix is to create extract in Desktop V10.5 and re-publish the workbook with .hyper extract.