This is actually something that Microsoft has noted as well in a support document that they have not tested Office for Mac 2011 in High Sierra yet, and that support for the 2011 version will also be coming to an end on the 10th of October, 2017. “Word, Excel, PowerPoint, Outlook and Lync have not been tested on macOS 10.13 High Sierra, and no formal support for this configuration will be provided. All applications in the Office for Mac 2011 suite are reaching end of support on October 10th, 2017.”
In AppleInsider’s testing, they found that when using the latest version of Office for Mac 2011, they noticed that there was a lot of crashing, user interface oddities, and that uninstalling and reinstalling the apps did not seem to help. Like we said, ultimately this means that if you do plan to upgrade to High Sierra, you might want to consider the newer versions of Office for Mac.
That being said, AppleInsider also noted that the latest build of Office for Mac 2016 isn’t quite perfect either as they did run into some issues, but nowhere quite as bad. However it is more than likely that Microsoft will eventually sort this out for when High Sierra is released later this year.