For some reason the --force flag does not work. It seems to get ignored completely.
I had this issue a while ago already (Npm install force) and decided to move on to another provider. However, I wanted to try it again as I really liked the idea of render but it seems that nothing was changed.
If the service you are referring to is a Static Site and you are trying to manually install dependencies, you will need to use the SKIP_INSTALL_DEPS environment variable (set to true) to override the default behavior.