Chart formats get corrupted

Hello

We are having an occasional issue, where chart styles get corrupted. In these instances, any charts created in a new location, or existing charts in a new location, get corrupted. The chart design options you can choose from all get corrupted, and the chart shrinks to a tiny square on the screen. Strangely, charts created within a regular Excel tab seem OK. Has anyone encountered this before, and/or knows what to do? It seems to happen when there's a change in internet connection, e.g. working from home or a cafe. (I don't seem to be able to upload a screen shot - don't have permissions apparently)

Thanks

Oliver