@Gavriel Well, from my experience with Tp-Link products for years as a consumer and as a computer engineer, I'm sorry to say more to myself that your RE450 device is defective in the 5GHz band...

@Gavriel I think your RE450 may be having a manufacturing defect in , I recommend looking for Tp-Link support and checking it out, but first one more tip from me... set the 5GHz channel to 36 and...

@Fool89 it will probably work now

@Fool89 Well, have you tried resetting both devices? both the repeater and the router? and try again to configure both from scratch?

@Fool89 sincerely try to remove all these static IPS, put everything on automatic and redo the configuration and return here with feedback, if it solves the problem or not... I'm waiting.

@Fool89 Strange that, do you use any MAC filter? Or set a specific IP on the network for your devices?