So the issue is that it it is encountering a stream discontinuity as a result of those ads Fubo is placing.
This basically EXT-X-DISCONTINUITY tags and indicates a complete reset of the stream, with a new stream following afterwards. This is something not handled well by streamlink unfortunately, so maybe looking at other alternatives.
EDIT: just looked at some other streams, while they have the EXT-X-DISCONTINUITY-SEQUENCE tag in the HLS, it appears Fubo isn't sending other ad streams, thus causing a reset of the stream. Guess this will need more investigation