Delayed ring of alarm clock

I use the default (preinstalled) clock app to set an alarm. It always works in the sense that the alarm sound rings. Sometimes however (maybe 1 of 5 days), it is delayed by up to five minutes. For example, when I tell the app to wake me up at 8:00, the first ringing might occur not before 8:04 – according to the phone’s own clock!

Just to anticipate the obvious question: No, it’s not me sleeping too deep. I often wake up by myself few minutes before the usual get-up time and then wait for the alarm. The device being used is a Teracube 2e from the Murena shop. Anyone else facing this issue?