Redmine

Hello
I have just upgraded in 4.2.6 and it works all fine except API request.
Some of my users used to call REST API via Excel to crete and update issues
It worked fine in 3.4.3 but now, create issues is ok but we encounter the following problem :

POST XML synchron (create issue) => OK
     POST XML asynchrone (create issue) => OK

POST JSON synchrone (test watchers.json) => KO
     POST JSON asynchrone (test watchers.json) => OK

PUT XML synchrone (update issue) => KO
     PUT XML asynchrone (update issue) => OK

It seems that synchron calls are uneffective.
Any ideas ?