I queried this with the council and received the following response:
To clarify on the cycle provision within Broadgate the restrictions in place currently allow cycling in all directions through the square and cyclists are permitted to gain entry at the two access points.
You are however quite correct that the regulatory signage at the High Street access point does state No Entry and does not have the appropriate "Except Cyclists" supplementary plate associated with it. This supplementary plate was omitted as a departure from standards to maintain the decluttered look within the area and negate the need for larger street furniture to be provided to accommodate the larger sign plate.
Therefore whilst you are right that technically the signage in place does provide a mixed message to cyclists, extended observations on site clearly show that cyclists are choosing to freely use Broadgate and we are not aware of any issues where cyclists have deviated from their chosen route because of absence of this supplementary plate.
Accordingly the intention is to monitor the new layout to determine whether this omitted sign plate is an specific issue, and should this be identified then appropriate action will be taken to mitigate this issue.