Why does it fail to connect to the server with Owncloud?

Question

Data synchronization

I installed a virtual machine with OwnCloud from bitnami on Vmware
, it
has ownCloud 9.0.2 (stable)
When I start the virtual machine, it first synchronizes everything normally, and then when I upload more files to a local folder on Windows after a while, it writes Unknown erorr
And the ownCloud server from the browser is not available, only rebooting it helps.
Nearby is the same ownCloud on the virtual machine, only the old version and everything is ok.
I don't update the version of the client on Windows 2.1.0 for compatibility with the old server, can there be problems because of this?