Go modules finding/downloading hangs

I’m having an issue where my Go application will hang whilst downloading/finding Go modules.

Eventually, it will timeout with the message:

No output has been received in the last 10m0s, this potentially indicates a stalled build or something wrong with the build itself.

Check the details on how to adjust your build configuration on: https://docs.travis-ci.com/user/common-build-problems/#Build-times-out-because-no-output-was-received

Any ideas what would be causing this? I can get it to build on macOS and Linux.