Whether any matter could be heard by bench consisting of members less than 3 as set out above

Yes, in the absence of a Member in any Bench due to vacancy or otherwise, any appeal may, with the approval of the President or, as the case may be, the State President, be heard by a Bench of two Members. Further, where the tax or input tax credit involved or the difference in tax or input tax credit involved or the amount of fine, fee or penalty determined in any order appealed against, does not exceed ` 5 Lakhs and which does not involve any question of law may, with the approval of the President and subject to such conditions as may be prescribed on the recommendations of the Council, be heard by a bench consisting of a single member.

(ICAI FAQ PUBLICATIONS 06-09-2017 Constitution of Appellate Tribunal: FAQ NO. 28)