A similar question has been answered here, but I'm sure there is no harm if others want to add more answers! https://www.al-islam.org/ask/can-any-spiritual-leader-claim-that-he-has-the-authority-to-forgive-the-sins-of-a-person
It seems as if you may have a specific spiritual leader in mind. Anyway, I don't know who it is, but no, they don't have the authority to forgive even one sin of a person let alone all of their sins. It sounds like they are playing psychological games or perhaps they are genuinely confused. Sometimes people who go heavily into mysticism become a little deluded or psychologically unbalanced and believe things about themself or their spiritual capabilities that are not true, this is not to say it is bad to go into mysticism and 'irfan but just that there are some dangers associated with it that it is good to be on the lookout for with respect to one's self and those one looks to for spiritual guidance. You should not trust wholeheartedly someone who claims to be able to forgive peoples' sins.
Also as a general rule it is always wise to keep one's eyes open around spiritual guides (as you are doing), there is no harm in taking the good from them and benefitting from whatever good they have to offer, but some people treat their spiritual guides as if they are walking gods and infallibles and no human being, except the prophets and Imams, can live up to that. Unless someone is in a complete state of denial, it often leads to a letdown, abuse, or loss of faith, because they are human beings. Anyway this may be veering off topic, wishing you the best in your spiritual pursuits.