White holes in xymon graphs

Hi,

can anyone explain those (white) blackouts in the attached xymon graph? I see no messages
neither in the client nor in the server logs.Those blackouts happen at different times:The duration is ~ 10 minutes = 2 intervalls?

Any hints?
hjb

[Anhang "hobbithole2.pdf" gelöscht von Hermann-Josef Beckers/Kreis-Steinfurt]