Bug appears to be an AntiGameOrigin problem as it does not display the number for empty cargo bays. I used IE as a control, which doesn't have AntiGameOrigin. I have seen this problem on Firefox and Chrome with the AntiGameOrigin add-on/extension. The number was shown correctly on IE but was replaced with NaN for Chrome and Firefox. Haven't tried Opera. I didn't see anything regarding this in the Forums.
Ogame Version: 5.7
Chrome Version: Version 60.0.3112.113 (Official Build) (64-bit)
Firefox Version: 54.0.1 (32-bit)
OS: Windows 10
Service Provider: Unknown
Ogame Version: 5.7
Chrome Version: Version 60.0.3112.113 (Official Build) (64-bit)
Firefox Version: 54.0.1 (32-bit)
OS: Windows 10
Service Provider: Unknown