There are multiple reasons which can cause bucket issues. Bucket issues need to be investigated in a logical and reductive approach. They can either be general issues - things that relate to problems with the farm or individual machines, scene specific issues - problems that relate to something in the scene, or a mix of the two. Here are several key steps that can be taken to identify the issues.
restart the farm and/or the DR machines.
check network drive availability
add a vray_dr_bucket element, switch off vray VFB and render the image in order to find if specific machines are causing the problem and what they are. Check here for details
once machines are identified discuss with people dealing with IT to see if there might be a software issue with these specific machines - could be any of - broken installation, missing SP, missing plugins. Work with IT to identify the problem.
IT - check that max is installed correctly with all plugins and service packs. Service pack mismatch is a very common problem. Here is how to check the service pack version through Deadline.
check your maps are all available on the P drive. if your maps are on R: drive check they are accessible in all locations UK, BG, AT
are you using any exotic plugins that might not be available on other machines. Be particularly mindful of Forest Pack
do you have modifier stacks with settings that are only affected at 'render time'. read here for more detail on modifier stack dependencies.
do you have any body objects. this is related to the previous point
overlapping geometry - very common cause for bucket problems
any shaders and maps NOT supported by v-ray. Normal Bump is the latest culprit. Click here for detail on how to troubleshoot shader issues using Modifier Zorb script.
check any geometry for issues like bad verts, overlaps, animation etc. For best practice click here.