- I don't think you have any significant speed gain if you stop the graph and even disconnect pins
- The error is not really COM+, the codes overlap and this error has a different meaning (what is the code exactly?)
The only way to eliminate all artifacts and smoothly swap the files and make it quick is to split the pipeline into parts and have video renderer in the filter graph you never stop and disconnect. This takes you back to bridging, or instead to similar technique of synchronization streams between upstream file graph and downstream presentation graph.
UPD. The error is 0x8004020C
VFW_E_BUFFER_NOTSET
"No buffer space has been set.", use ShowHresult to decode codes, this tool has in particular priority to DirectShow codes when it hits overlapped code blocks.