I noticed that several alerts related to tablespace full were sent from OEM every collection schedule. At first sight I thought this may be related to OEM itself but after spending some significant time in MOS found a bug note stating that the 2017 April PSU patch was responsible.
The issue is that dba_tablespace_usage_metrics is not accounting for autoextend datafiles. So even if you add a new datafile, your used space will continue be reported as it was before.
You need to apply patch 26198757 on top of April PSU.
Hope this help you to avoid all this noise and happy patching.