Wifi access points are 2.4GHz normally. Is there a set of cordless phones operating around 900MHz in the household?

The EU models/units operate on a different frequency than US models and are labeled RUxxx vs TSUxxxx.

If you have a TSU7X00, it is set for US frequency and cannot be changed to EU frequency.

To verify which one you have, you can touch and hold the setup (remote icon) at top left of the screen for 3+ seconds and you can see exactly what model you have as well as the firmware version that is loaded.

TSU7000 will only work with an RFX6500 that is the US model on the same frequency (IIRC, is 910MHz).