One way you can workaround this issue is to filter out events coming from that mount point. There's a good example in the documentation, see https://www.elastic.co/guide/en/beats/metricbeat/current/metricbeat-metricset-system-filesystem.html#_filtering. Most of the mount points in that example are not useful to report on so this is a good option IMO.
You could also setup a filter with a condition like when system.filesystem.files == 18446744073709551615, drop_event. Or your could just drop the system.filesystem.files field.