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That sounds like a problem with the key mechanism sticking, for that one key. Or the keyswitch under that one key needs replacing, for sticky contacts or a similar problem.
Compressed air blown into a keyboard where and around where there is a problem key, can sometimes cure the problem; It's worth a try anyway.
After that is the question of whether you would wish to undertake repairing/replacing that key, or the keyswitch mechanism under it, yourself, or would prefer to hire a keyboard repair professional in your region to do the repair.