I have found a workaround to the issue of the mobile processing lab not being able to produce Rocket parts from metal.
There seems to be an issue with the ScienceLabs.cfg, For version 4.0.99.32, by removing this file and then replacing it with an older config (in my case Version 4.0.2.6) it fixes the issue and allows the science lab to produce rocket parts again!
images of science lab not working with new config and it working with old config (I have tested it and it seems to work as intended with no issues)
New config on top, Old on bottom.