client.set({vixitor.xx:yy}) sometimes fail to update in Chat sidebar

I implemented APP to update visitor information once chat is opened.

It worked in my environment but it sometimes fails to update some field in some customers environment. Not sure what's the conditions..

Here is the source code:

client.set({
  'visitor.name': 'aaa',
  'visitor.email': 'bbb',
  'visitor.phone': 'ccc',
  'visitor.notes': 'ddd'
 }).then(function (result) {
   console.log('result：' + JSON.stringify(result));
 });

Here is sample error:

{
   "errors":{
      "visitor.name":{
         "id":"13221074.1CClGKVmCEMmTJx",
         "__status":"failed",
         "path":"visitor.name"
      },
      "visitor.phone":{
         "id":"13221074.1CClGKVmCEMmTJx",
         "__status":"failed",
         "path":"visitor.phone"
      }
   },
   "visitor.notes":"ddd",
   "visitor.email":"bbb"
}

The fields which is failed to update are not fixed.

Sometimes only notes, sometimes success.

Before calling client.set(), APP calls client.get(visitor) to fetch visitor's information and 100% success, which means client itself works correctly.

Kindly give me some advice to avoid the errors.

Thank you