Invalid stellar address when trying to send XLM to Kraken account

Hello,
i tried to send some Lumen to a Stellar XLM deposit address generated on my kraken.com account.
The QR is recognized correctly (address + memo), but a red alert shows up under the address on Keybase Mobile App:
"Invalid stellar address".
This way I am not able to move my XLM to somewhere else.
Any idea why?

Start by reproducing the transfer in the Keybase Mobile App using a Kraken-generated Stellar deposit QR code, checking the decoded address and memo against the app's validation behavior. Determine why this address is rejected and document a confirmed fix or the precise incompatibility, with a regression check for the reported QR flow.

Written by the indexing model from the issue text.