space group Binding: not all group members are added to bonded space

[Jihed525]

steps:
create 2 spaces :space testA/Space TestB
both spaces have binding rule to group users
import +5000
while import is ongoing, post & publish article in space TestA + delete binding and add it it again for group users

Actual behavior
At some point, some errors in server log are displayed " Problem occurred when saving user bindings for user" and related user isn't added to space

Expected
all group members should be added to binded space

related eXo task : 75828

[margondicco]

@srenault-meeds in progress