I found the same behavior that multiple Webi report recurring jobs "to be generated in excel format for some days it is fine but unfortunately the report is scheduling in Webi format instead of excel format" since DST change on 3/13/2016.
When this scheduled as Excel but turns out as Webi behavior occurs, that running job would hang forever unless I terminate it by delete it in CMC.
My workaround is to reschedule those recurring jobs on the user behalf and rerun it. So far, I have reschedule/correct more than a dozen recurring jobs. No recurring jobs in Crystal Report or Deski report type has this problem, but Webi.
I found this problem on BOXI3.1 SP7 + FP 7.1. No similar issue found on BI4.1 SP07.
Regards,
Jin-Chong