@kerri-r If you have troubles to connect your new RE to your router try this post suggestions.

@Karisy I would reset the REs to their factry defaults and use the WPS method for configuring - details. If no improvement try this troubleshooting guide for your particular case. If that doesn't...

@ppt3 I see that you're using a regional FW release (DE). In this particular case it's best to contact your local support for advise.

@Abderr77 According to the support portal there's an intermediate FW version that you have to go through: If your target is TD-W8961N(EU)_V5_230928 try downgrading to the intermediate version first...

@KarloVranjes It appears that there's a newer FW release for your modem router - Archer VR2100v(EU)_V1_1.16.0 Build 260124 - here. Have you considered updating the VR2100v FW and test if that...

@ACCSA_FER If you have (US) region FW try this FW release - Archer C80(US)_V2.20_1.14.3 Build 241025.