I have a BR340 switch that after rebooting it it won't connect any faster than 4 gbps.
Please paste 'licenseshow'
Maybe you lost 8G license which is required on Brocade 300 for 8Gbps speed.
I think you might be on to something there. We just split two br340s in to two seperate fabrics. I just looked at the license and one shows 2 8 gig fc liscenses and the other shows none.
at the moment 8gb License is a standard in 8gb switches
run command sfpshow and check if Vendor PN number doesn match4gb models
also check second end (hba,array etc)
Yes, it's standard but there is one model which is not true - Brocade 300
Same as 6510 doesn't need Full Fabric for E_Ports, but 300 or 5100 still need this license regardless of FOS version - even in 7.2.x