Apparently, there are no SpamBlacklist or TitleBlacklist entries for the user, so that's not a possible explanation.
Some or all users are sometimes or always unable to make multiple edits in an unknown span of time. It would appear the rate limit functionality is loosing track of time. As such, it is observed numerous times that edit attempst by end users are rejected when in fact they have (far?) fewer edits and only over a long period of time.
Root cause as of yet is unknown. It could be in the Core ping limiter logic, it could be at a higher level in the API/Revision/PageUpdater layer, or it could be at a lower level e.g. in the BagOStuff abstraction, or perhaps lower still e.g. in Memcached itself and/or atomic particles somewhere in-between influenced by solar rays.