It may very well be a bug but that is not certain, or at least not demonstrated, quite yet based on the details you have shared let's look into it a little.
- Did the server ever work before on the same device and same OS? If so has anything changed since then?
- Is the server properly configured (https://forum.xda-developers.com/t/mixplorer-q-a-and-faq-user-manual.3308582/post-65157350
), in particular the need to create an account (user with credentials) and use matching port number (sometimes manual entry required for port) and properly matched server url prefix and security settings (TSL/SSL) Note: my experience and the documentation is based on FTP; much but not all of it might apply to HTTP server.
- In MiXplorer on the device where you run the MiX server, can you read and write to the same folder that is set as home location for goodsync windows client?
If the server is properly configured and you can write files locally in MiX in the folder that MiX assigns as home to the server, this may be a bug in which case, as described in the opening posts of this thread, please log it and share the log in the main thread with a description (a detailed list) of what actions were taken while reproducing the issue and logging it. More helpful information about logging here: https://forum.xda-developers.com/t/mixplorer-q-a-and-faq-user-manual.3308582/post-65157367
BTW, it is nice that you can log this from the client side (I use Filezilla for that with FTP). It is primarily the MiXplorer log which will tell the developer what MiXplorer is doing but the details from your client log might also help.