I use VS Code with Salesforce extensions and connect to my sandbox as explained here:
With my package.xml I fetched apex classes and custom labels from sandbox.
In settings I enabled push-or-deploy-on-save.
On saving and deploying I always get error messages where custom labels are used: "External string does not exist: MY_LABEL":
static final String MY_LABEL = Label.MY_LABEL;
My custom labels exist in the sandbox and in my project, so what causes this error?