Thank you for reaching out!
Could you share more details about your configuration? Are you using RS232 Over IP function? Are you using VPN Hub on RMS?
Just to clarify, two-way communication with the PLC works, it's only an issue when a file needs to be uploaded, correct?
Also, if possible, please attach a Troubleshoot file from the RUT955 so I can see your configuration. Troubleshoot file can be generated by navigating to System → Administration → Troubleshoot. It will only be visible to Teltonika moderators.