WARNING:x4kma:423 - The following signals, driven by buffers or logic that reduced to a buffer, drive closed FMAPs. You may open all closed FMAPs by setting the environment variable XIL_MAP_OPEN_FMAPS.
This warning is saying that there is some logic that has been reduced to a buffer (nothing) that could be merged into a particular FMAP, but the FMAP is closed. So there will be an extra level of logic that could be avoided had the FMAP been open.
"Closed" indicates that the software cannot add or remove logic from the function specified by the MAP symbol.
A workaround is to set the XIL_MAP_OPEN_FMAPS environment variable, which will set all FMAPs to open.