I've just installed an SXT LTE kit (Mikrotik model R11e-LTE) which seems to be working fine EXCEPT... if I send or receive WhatsApp pictures I can get the thumbnail but not the full image.

I've been Goggling and trawling this forum and seen other threads but don't understand the suggested solutions.

I have reset the config on the box and still have the same issue. I know its not my ISP as there is no problem using WhatsApp if I put the SIM into my old Asus 4G router.

Appreciate any help! I'm new to this system so at a bit of a lost how to proceed.

I guess that you by have gotten the news that facebook and whatsapp have /have had problem with their images..

Yes thats funny. All my customers where i installed some wifi devices told me yesterday the WLAN does not work anymore. In fact they couldn't send or receive pictures with whats app... Yes, if FB services does not work anymore they judge the whole internet or the local wlan does not work in general....

Your "bad luck"! Installed internet access on that day! Not Mikrotik device fault!