XMR not connecting "Unable to Subscribe"

My two displays I have set up to test are no longer connecting to the XMR server. They were apparently working for the past few days, but now are logging Unable to subscribe: : Length cannot be less than zero.

Here is a snapshot of the initial logs which include the problem entries:

UI Thread|9/12/2019 12:56:28 PM|Info|MainForm|Client Initialised
RegisterAgentThread|9/12/2019 12:56:28 PM|Info|RegisterAgent - Run|Thread Started
RegisterAgentThread|9/12/2019 12:56:28 PM|Info|RegisterAgent - Run|Thread Woken and Lock Obtained
ScheduleManagerThread|9/12/2019 12:56:28 PM|Info|ScheduleManager - Run|Thread Started
LibraryAgent|9/12/2019 12:56:28 PM|Info|LibraryAgent - Run|Thread Started
RequiredFilesAgentThread|9/12/2019 12:56:28 PM|Info|RequiredFilesAgent - Run|Thread Started
LogAgent|9/12/2019 12:56:28 PM|Info|LogAgent - Run|Thread Started
XmrSubscriber|9/12/2019 12:56:28 PM|Info|XmrSubscriber - Run|Thread Started
XmrSubscriber|9/12/2019 12:56:29 PM|Info|XmrSubscriber - Run|Unable to Subscribe: Length cannot be less than zero.
Parameter name: length
RegisterAgentThread|9/12/2019 12:56:29 PM|Info|PopulateFromXml|XML configuration for [AggregationLevel] which this player doesn't understand.
RequiredFilesAgentThread|9/12/2019 12:56:30 PM|Info|RequiredFiles - ReportInventory|Reporting Inventory
RegisterAgentThread|9/12/2019 12:56:30 PM|Info|PopulateFromXml|Unable to write [Item].
RegisterAgentThread|9/12/2019 12:56:30 PM|Info|getDateFromHi|Unable to parse H:i, Error = Input string was not in a correct format.
RegisterAgentThread|9/12/2019 12:56:30 PM|Info|getDateFromHi|Unable to parse H:i, Error = Input string was not in a correct format.

The connection is streamed through a secondary NGINX server (on a different VM from the one running docker and the Xibo containers), this is the configuration I made (was working a day ago fine):

server {
        listen 9505;
        proxy_pass [redacted xibo docker VM IP]:9505;

}

The Xibo install (2.1.0) is via Docker.

Thanks for any help.