I heard about issue with Vendor join but trading center doesnt show anything which happened to me (first screen shot), then another vendor joined and i got notification of old and new vendor twice and i have 2 of each vendors and trading center show their items (screen shot 2)
1 and 3 are same and 2 and 4 are same but another vendor
when i clicked my towers to check the progress of building it i got the following
Thank you for your support and help