IQ connect low available space on X5

Have 2 garmin watches an X5 and a 5 plus.

The issue is when looking at available storage for apps watch faces and data fields.

Both watches have 1 watch face And 2 new data fields from the store.

The x5 shows available space is 1.91mb

The 5 plus has over 12mb

When I asked Garmin Support I was told it's to do with the different Firmware of each watch ?

I Find this hard to imagine, any ideas.

Graeme