We have two nodes (701 and 702) of PRPC 7.1.7 sharing the same PegaDB.
At times, we have issues with missing css on the 701 node. Not sure what causes this issues, but the way we fix this is to log on 702 node, and launch the same application. This somehow fixes the css on 701 node.
When missing CSS, all Pega users will also experience the issue.
I think this may be related to a known issue with the activity pzDeleteOrphanStaticContent (called by the agent "DeleteUnusedStaticContentFiles) where it can intermittently delete static content which isn't actually unused. I believe in 7.1.7 this is addressed by HFix-22715.
I would submit an SR with GCS to have this investigated and the hotfix provided (if appropriate).