Normally RAM will downgrade and not cause any problems. However that's not always the case and unfortunately you can usually only trouble shoot the problem by trial and error.
But a good first start is to run memtest and see if you are getting errors. If memtest finishes full 100% with no errors then you should be fine.
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But a good first start is to run memtest and see if you are getting errors. If memtest finishes full 100% with no errors then you should be fine.