BlackBerry Forums Support Community - Blackberry Device Connectivity

I have a query and wonder you guys can help ?
It's a bit complicated so please bear with me..............
I work for a company with around 300 devices connecting to a hosted BES (by a third party). The devices we use range from the 9000 all the way to the 9720 (no BB10 devices though). With regards networks we use Vodafone & EE.

Right now down to the issue. The problem we are experiencing is that numerous devices seem to be losing connectivity to our hosted BES, this seems to occur when they automatically lock (after the 10 min timeout). I can tell this is because the network mode goes from upper case to lower case when it locks. This means the device does not receive mail etc... however as soon as you login the network mode goes to upper case and mail gets downloaded. I have tried testing this on a standalone device not connected to a BES and the network mode stays uppercase all the even when locked, so it appears to be a policy issue. I have contacted our suppliers who cannot seem to find a solution and just tell me the wipe and reactivate the device, unfortunately this has happened over 50 times now.
In addition I have another issue which may be linked to the above. If the devices stay locked for a couple of days it totally loses connectivity to the BES and if you try and enter the security pin password it won’t accept it, this means you have to wipe and reactivate the device.

I have tried using the latest sim cards and updating the OS to the latest version but I keep on getting this issue.

I know this does sound weird but I've seen it for myself and since I have no access to the BES I can't tell whether it's a network, device or BES/policy issue.

Can anyone please help ?