How to restore stock firmware on a TP Link RE450 v2?

I want to go back to the stock firmware at my repeater TP Link RE450 Version 2.
Every method posted here in the forum did not work - I think these solutions only work for the Version 1 of the RE450.
Using a TFTP server over the network connector definitely does not work - I did not even manage to connect the RE450v2 to this server.
Using a TFTP server over the serial pads on the PCB is not really easy as it is for the RE450v1: You have to desolder the whole PCB and then two tiny resistors in advance.

So I ended up flashing a cut stock firmware image via the OpenWrt web interface.
Now my repeater is bricked: All LED are flashing simultaneously about every three seconds.

Does anybody know how to unbrick the repeater in such a case? Is it really not possible to get access via a TFTP-Server using the network connector?
Thank you in advance for your help!


U-Boot does not seem to have any recovery functions, so debricking requires connection via UART.