Hi. See here. (German Post)
As you are using a strato service I assume you can read it. 
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In short: as Cryptomator cannot know a path Limitation set by the sync client, you can either search for the long file name in the vault and shorten it (the unencrypted file), or you create a new vault, manually set a path limit in the json settings file, and copy your unencrypted files from the old vault into the new vault.
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