Vector Plans will sometimes be loaded with Unreadable Text.
This can be fixed using the Feature called "Rasterise Text" on the Vector Plan.
The option can be applied from one of the following ways.
Highlight the vector plan on the Plan Tab and the details window check the Rasterise Text option.
Then you close and Reopen the plan to see the changes.
If you notice that all the plans you insert are having the same issue then this setting can be turned on in the Cubit options level so that any Vector plan you insert will automatically have this setting applied.