i managed to interecept it, this is the request/response:

["REQ","OJ957lpN",{"#e":["d8318134bc5f45280e9e88f413972733b7684f18e12d995f2c791db7f46bdd8c","4eb0e2b8d2b496ead92bb58cdf38baba9cfc2ed95c2ec83fbe880b3ac26cede6"],"kinds":[9735]},{"#a":[],"kinds":[9735]}]

["NOTICE","invalid: must be greater than or equal to 1 tagValues at \"[3].#a\""]

(it could very well be nostrudel making an invalid request, but can't remember seeing it from other relays)