Exec command fails if running longer than 30 minutes

The following script fails when started using /api/endpoints/envid/docker/exec/execid/start

```
#!/bin/bash
# Wait for 31 minutes (1860 seconds)
sleep 1860
echo "31 minutes have passed."

```
29 minutes are working.

The HTTP Request returns the error 502. This problem only occurs when using the Portainer Agent. It runs successfully when using the Docker socket.
