I’ve been dealing with the same problem for a while. But I guess I just fixed it.
The solution doesn’t make much sense to me but it works like a charm.
I placed the dateSource parameter on two places in the Reflect call, like this:
&dateSource=`myTvDate`
&dittoSnippetParameters=`parents:7|dateSource:myTvDate|sortBy:myTvDate DESC`
So this is what my Reflect-call looks like:
[!Reflect? &dateFormat=`%A %e %B %Y` &dateSource=`myTvDate` &getDocuments=`1` &extenders=`dateFilter` &tplContainer=`refAgendaContainer` &tplMonth=`refAgendaMonth` &tplMonthInner=`refAgendaMonthInner` &tplYear=`refAgendaYear` &tplYearInner=`refAgendaYearInner` &tplItem=`refAgendaItem` &dittoSnippetParameters=`parents:7|dateSource:myTvDate|sortBy:myTvDate DESC|myTvDate:agendaDate,@EVAL return strtotime('-1 day');,6` &id=`ag`!]
I guess the bare minimum should be:
[!Reflect? &dateSource=`myTvDate` &dittoSnippetParameters=`parents:7|dateSource:myTvDate`!]
Hope this does the trick for you too!