Tado app NOK on iPhone XR but works on other devices ... ?

hi everybody,

anyone able to help with this strange phenomenon :

I have Tado app running on a (very) old iPhone (model 9?), on my iPad and also in Safari browser on Mac + also on my daily usage iPhone XR.

all four connections worked perfectly since months, not an issue at all (and very happy with Tado !!)

but since a few days, the app on the iPhone XR bugs : it launches but remains on a full orange screen with the wheel turning at the bottom of it. it never goes further. At the same moment, it works fine on the 3 other devices, the problem is only and only on the iPhone XR...

I tried to kill the app and relaunch it, it tried to disconnect/reconnect, I tried another wifi or no wifi at all (4G), shutting down the iPhone, I even deinstalled the app and installed again, still the same ... )-:

any idea ?

thanks beforehand,