Starting a secondary database in a replica set generates Network Interface Exceeded Time Limit errors

We have a replica set and the secondary and primary are in sync and all is good. We had this running to days without any issues.

After 7pm each evening we stop the secondary database instance, backup the server and then start it again. The secondary database instance then eventually catches up. This has worked for the last few months without any issues.

Now, when the secondary database instance is restarted we get network timeout messages over and over again and the secondary gets further and further behind.

We have no idea what causes these timeouts or how the timeout can be increased.