History broken after cleaning up old data with trimhistory

good day all,

my xymon 4.3.28-1.el7.terabithia running on Centos7 has encountered a problem since i made a cleanup using trimhistory command.

If a test (i.e. conn or anyelse) has been failing for a few hours, clicking the History Button shows all green bars, no red bars for the KO period.

The bars show red lines for previous failures only until the time i used the trimhistory.
What is the possible cause and solution?

I issued this command:

/usr/libexec/xymon/trimhistory --drop --droplogs --dropsvcs --cutoff=`date +%s --date="1 Oct 2018"` --env=/etc/xymon/xymonserver.cfg

Thanks in advance!