Some advanced functionality was accidentally removed from TDataFrame during its upgrade to RDataFrame, namely the possibility to cast RInterface<TFilter<...>> to RInterface<TFilterBase>.
It turns out that users were relying on that functionality, making the switch to v6.14 problematic.
A general, user-friendly solution (PR 2182, "[DF] Add common base class to all node types") will be available in master as soon as
ROOT-9236 (issues with jitting on 32bit archs) is clarified/worked around/solved.
v6.14 might either adopt that solution or re-introduce the cast operators for RInterface that have been removed by commit 693dba9fc8.