@AGallo Are both routers MR6400 v4? What is the firmware version of that one purchased in 2019, and what is that of the one purchased in 2020? Are they working with the same SIM card carrier, which...

@Jazzy71 Have you checked this thread? https://community.tp-link.com/en/home/forum/topic/241534

@Krishankum59 Do you mean the SIM card cannot be detected? If that is the case, check this article: https://community.tp-link.com/en/home/forum/topic/261882

@cayc The engineer will help confirm if it can be downgraded.

@Internet-san Can we know the WAN connection type on the AX73? Have you observed this when you first install the router, or this happens recently?

@cayc Sorry to know the firmware update caused issues to the connection. We would like to escalate the case to the support engineers, they will help analyze the issue and fix it.