I have had this a number of times on various bikes, I always overcame it but it took time and was a pain. Have had lots of different bleeding tools, including a power bleeder, but the only thing I have found always works is the vacuum bleeder that pulls the fluid through from the caliper….there are plenty on amazon and eBay, but they all seem to have bleed hoses that are too big, so a bit of jiggery pokery is required.