PS:
In and out, aka connecting and disconnecting often improves a lot.
In Germany we have "große Tuckel", aka " Großtuchel" for Mics. This is
a
connector that will clean the contact areas with "knife". For PCI and
similar slots not only corrosion is an issue, but also ground vibrations
can cause problems.
I experienced that alarming issues could be solved by remounting the
hardware.