Postie stopped working processing automatically

we have worked with Postie for a couple of weeks, since yesterday the e-mails aren’t checked and processed according to the “Check dor mail every” setting (5 minutes in our case). When I do a Test Config the result is ok and there is a message how many messages are waiting in the mailbox. If I start Postie manually (Process Email) the messages are processed. So it is working but not every 5 minutes anymore. What can be the prolem?

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