Hi, the issue I believe is the Brit Box is using the filmon streams, which used to be free and are now not - so box is probably accessing these for a couple of mins, before getting booted off, by filmon. If this is the case, not much can be done about this.
The issue is the Britbox is a fudge of a few applications/systems, some of which are not working as they were a couple of years back - firstly there are no free to air IPTV terrestrials (officially) & secondly Britbox was (is?) using a load of Kodi (formerly XBMC apps) many of which are not supported anymore. Basically a custom solution with a number of old or unsupported applications, which ultimately is likely to cause user issues or simply non-functioning services.
I am not entirely sure if this is a workable system anymore? For free to air, satellite system, one-off may be a good option for you - if looking for an IPTV solution or more premium type content as well, the likes of the Britbox have been surpassed with newer equipment and hosted services, which do the job better and easier. Main difference is new IPTV hardware is not a fudge of services, much more like Sky/Freesat, a single integrated solution - no multitude of various applications to watch TV - bypassing these 'get it for free' but rarely work, type of apps - which are ok for 5 minutes.....
Paul
http://www.televisiontechnology.eu966783944