If you are running a version of Nintex Foxtrot RPA that is 15.1.7 or below, and it seems that all of a sudden the bot won't connect and you do not know of any changes that have been made to your environment, it may be that a very recent update to Office is conflicting with your Foxtrot version leaving it in a frozen state on the Starting screen.
Our Development Team is aware of the conflict and they are working with Microsoft to determine what they changed that "broke" the older versions of Bot.
We believe that upgrading your version to version 15.1.10 will fix this issue as we have seen multiple customers upgrade and this worked for them. (Downloads for version 15.1.10 are below).
An alternative to upgrading would be to revert your system back to the point before the update happened and suspend the option of updating until we know if this can be fixed on either our end or Microsoft's. Since we always suggest that you upgrade to our newest version, we believe that an upgrade to v15.1.10 would benefit your company in this way as well as with the features added and bug fixes resolved already in that version.
If you want to see if the Office update was installed on your machine, please go to Programs and Feature's, Microsoft 365 and look to see if the version is 16.0.14131.20278. If it is, you should be able to see when it was installed (starting the first week of July) and can make a decision based on the two suggestions above.