At https://github.com/nuxeo/nuxeo-ui-elements/blob/maintenance-2.4.x/nuxeo-user-group-management/nuxeo-user-group-permissions-table.html#L296 there is a missing space.
The consequence is that the built query looks like below in the JSON payload
{ "params": { "query": "SELECT * FROM Document WHERE ecm:mixinType != \"HiddenInNavigation\"AND ecm:isProxy = 0 AND ecm:isVersion = 0 AND ecm:isTrashed = 0AND ecm:acl/*1/principal = \"thierry\"", "page": 0, "pageSize": 25 }, "context": {} }
Same problem in master: https://github.com/nuxeo/nuxeo-ui-elements/blob/master/nuxeo-user-group-management/nuxeo-user-group-permissions-table.js#L299
Note that it seems to works 2 times out of 3 even with this problem.