Missing LR1110 Transmissions

We are using the LR1110 and the Modem-E firmware to send packets of data. We have set the chip to transmit every 45 seconds. This is within the on-the-air policy for Europe. When monitoring the data received at the gateway, the packets, at random, are detected with time delta’s of 90 or 180 or 270 seconds and then restarts again. The FCNT data is sequentially correct. There just seems to be stopped transmissions or gateway doesn’t detect for some reason.

Can anyone please help and give some ideas of where and what to look for.