Dynamically link and start/pause a filesrc to a running pipeline with a live source

The main branch of my pipeline:

audiotestsrc(is-live=true) -> audioconvert -> audiomixer(force-live=true) -> capsfilter -> queue -> wasapisink

When the pipeline is PLAYING I want to dynamically link the following branch to a newly requested pad of the audiomixer:

filesrc -> wavparse -> audioresample -> audioconvert -> capsfilter

The caps of both branches configured for the capsfilters are exactly the same. I use

gst_pad_set_offset(requestedSinkPadOfMixer, runningTime);

to achieve that the filesrc is played from zero position. My issue is that I have a few audio drop-outs immediately after linking the filesrc branch. I already tried to add an offset to the runningTime but this did not help. I figured already out that the dropouts occur in the audiotestsrc stream and not in the filesrc stream.

Do you have any idea how I can solve this issue?

Furthermore I would be interested in how I can independently pause and seek my filesrc without any impact on the main branch of my pipeline.