When switching to creative from survival on a multiplayer world i have not been able to open the command block UI, the only way to fix is to log out of the server then back in Notes:(Friends are having the same problems on same server),(Only seems to happen in MP Servers),(Seems to also affect LAN Servers)
Same bug as
MC-87925
Linked issues
Comments

As indicated in the report you linked, it is a duplicate of MC-87872. Please do not re-report existing issues. Note also this has been marked as fixed for a future release version.