munin drawing only chopped lines

[DawgG]

i run munin on the hosts in my networks and for some time now the server that serves the html-pages draws (almost) all the pngs for the graphs with irregularly chopped lines; i.e. for different periods of time there is no line/field in the graph. this is different (but similar) in all graphs; it is not that there is the identical period of time missing in all graphs.

i have re-emerged all pkgs related to munin and deleted all rrds on the server; the server itself was recently upgraded to more powerful hardware (Xeon L5630; 2X4 cores, 8gb ram). even though "Munin Processing Time" on the server itself shows a warning (processing time is about 260 sec; 300 means death) there are no warnings in the logs on the server.

the server monitors about 250 hosts over ethernet/fiber, but only about 60 of them run 24/7. i cannot run apache (or a "big" webserver) on the server so static generation cannot be avoided.

since the logfiles munin-update.log and munin-graph.log were huge (6gb each for 2 days) i changed the loglevel according to this http://lzone.de/How+to+decrease+the+Munin+log+level but i haven't waited to see if that changes anything yet.

the server is amd64 and everything is up to date.
THX for your help!
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DUMM KLICKT GUT.