I don't think anyone can tell you why this happens now since the root cause isn't known.
It's not a SQL Server issue, it's a Cluster issue. I would have thought you would have event 1558 in the system log - I'm pretty sure that is the text for that error. I don't know if you have a file share witness but I thought the error message was a bit different. Either way, you need to look for the event codes in the logs for the node where the problems are and look those up.
My first reply would still hold true and you need to do that. Did you check the resource? Is it available to all nodes? Did you check the permissions? Have any file system filter drivers been changed or added? Did you try to bring it online manually?
There were also suggestions in the errors that said:
Verify that the folders exist and are accessible. Additionally, confirm the state of the Server service on this cluster node using Server Manager and look for other related events on this cluster node. It may be necessary to restart the network name resource 'ABCSSQL' in this clustered service or application.
So you need to do all of those things.

Sue