Sounds like you got a dud. I’ve had really good luck with cheap Amazon servos for crawling.

Cheap. Waterproof. Durable. Strong. Not fast but that doesn’t bother me for crawling.

https://www.amazon.com/dp/B083GPMMYK/ref=cm_sw_r_cp_api_i_6J8XVD5YKH1SE5VPJVPE