I believe automations with names containing for examlple commas (',') are not able to use incoming email attachments. The email attachment is downloaded to a temporary folder like the example below where the name of the automation becomes a part of the path:
C:\\ProgramData\\Safe Software\\FME Server\\resources\\system\\temp\\emailattachments\\20211230112047-<Name_of_automation>-<Email_Subject>-7ac8a779-9ea4-4ab3-a228-c880ec539c95\\data_562_1715_20211013_0933.xml
Spaces in the automation name is replaced by underscore but a comma sign is not.
I am not using the option to download the attachment to a specified folder.
I got this error (with the triple dots added by me):
XML Parser error: 'unable to open primary document entity 'C:\\ProgramData\\Safe Software\\FME Server\\resources\\system\\temp\\emailattachments\\... analys,_uppdate...data_562_1715_20211013_0933.xml
Note the bold part with a comma in the path.
I renamed the automation and the problem was solved.