I am attaching the instructions for fixing traps for the McAfee Enterprise firewall version 8.3.2. These steps may work on other firewall versions, however I have not tested them on any version other than 8.3.2. Please feel free to download them and implement them to resolve your traps issue. Please identify them as resolving your 8.3.2 issue once you have verified they work.
I ran into the same problem you have. I opened a trouble ticket with both McAfee and with SolarWinds but neither one wants to accept responsibility for the problem. I have a workaround that I developed which can be implemented on the McAfee firewall. If you are familiar/comfortable with command line I can give you the fix I developed. As part of my trouble ticket with SolarWinds they updated the MIB database for the McAfee firewall, they thought that might fix the problem but I have yet to try the new MIBs. If you try the new MIBs and it still doesn't work let me know and I will provide you the work around. It is a little involved but it definitely will work.
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