Problem solving has with me

Had the Funkthermometer retour send unfortunately today, as it indicated to me just simply to 1,5 m distance from the transmitter, the temp.!
As soon as I have others and further placed ... whether the sender or receiver ... was lost radio contact!
It held only the temp display at one meter distance between patio door and the living room! So to speak, only one behind the door!
A Ask the recipient in the room on the table: reception away!
A change in the transmitter on the terrace a little further away: no more sending!
So I had not thought so after the customer recessions here :-(
Surely it is up to 868 MHz! Because the device does not have 433 MHz !!
Too bad!