I cant seem to fix a date/time issue when uploading my csv into AGOL. The date and times are all incorrect when uploaded under UTC, but I get errors in the files (i.e. they are inaccessible and will not open) when I try to change the timezone. Also, the files will only be used by individuals in working in the same timezone so conversion is not an issue.
In order to troubleshoot the issue you have described, I recommend reviewing the Work with date fields—ArcGIS Online Help | Documentation to confirm that the Date/Time format presented in you csv file aligns with the supported formats for ArcGIS Online.