Q. Is it better not to play musical instruments during a simchat bet hashoeva since it is done on chol hamoed?

A. Although, some Poskim are stringent in regards to playing musical instruments on Chol Hamoed (Shaar Efraim 40, quoted by Beer Heitev 534: 5), however, many Poskim are lenient as Shaarei Teshuva (ibid. 5) mentions in the name of Shvus Yaakov (1: 25), Shoel Umoshev (5: 3) and others.
Minchas Elozor (1: 29) writes that the minhag of Geonoim and Kedoshim was to play instruments during the simchas beis hashoeva, See similar in Otzer Haposkim (661: 2).
Horav Shlomo Miller’s Shlit’a opinion is to be lenient.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a