I'm using the TRB140 with the lastest firmware (EU). Whenever I try to enable the settings for ipv6, the wan connection goes down. The sim card works with ipv6 in another device, with the same APN settings. My ISP do provide ipv6 on 4G/LTE.
Also there is another problem that when I'm trying to go back to the default settings, the wan connection never resumes. The only way to get a connection then, is to insert the sim card into another device, and back to the TRB140 again.