Custom plugin Interval/Crondate turning purple quickly

I have a custom plugin that is set to run every Tuesday at 10am on the
server itself, that all runs fine and as expected, however it seems that
shortly after the task has reported back to Xymon (20/30 mins) the task
turns purple. I was expecting the status to stay green (or red etc) until
the next run time. Any ideas why this is happening?

Running Xymon 4.3.28 and the server side tasks.cfg looks like this:

[sometask]
        ENVFILE /usr/local/xymon/server/etc/xymonserver.cfg
        CMD /usr/local/xymon/server/ext/sometask.sh
        LOGFILE $XYMONSERVERLOGS/sometask.log
        CRONDATE 0 10 * * 2

This did happen last week when I originally implemented the task, but I
figured it was due to manually running xymoncmd... though that doesn't seem
to be the case.

Cheers