Cell doesn't load after client update to 2.5.6

[bencegal]

After Blizzard updated the client to 2.5.6, Cell no longer loads.

There are no Lua errors or other visible error messages, the addon simply doesn't load.

[TylerPentecost]

Seems to be working fine in version 5.5.4 (build 68571) for MOP Classic.

[sero2kk]

After Blizzard updated the client to 2.5.6, Cell no longer loads.

There are no Lua errors or other visible error messages, the addon simply doesn't load.

Same problem with TBC Classic - Cell Version r274-release and r277-beta doesn't load