Śabaras of Kauśika gotra
As per the Kaṭakarājavaṃśāvali (text based on traditional records of the Jagannātha temple), the descendants of the Śabara Viśvāvasu belong to the Kauśika gotra.
This might be connected to a statement of Aitareya Brāhmaṇa (see quoted tweet).
As per Aitareya Brāhmaṇa (AB), Ṛṣi Viśvāmitra cursed some of his sons to become Śabaras, etc. It further says that most of the ‘dasyūs’ were the descendants of Viśvāmitra.
The mention of Śabaras belonging to the Kauśika gotra seems congruent with AB.