keep contents of nofile buffer

My plugin creates new buffer, sets buffer type to nofile and fills it with text via job_start with out_io=buffer. Simplified code:

enew
setl bt=nofile
...
call job_start(cmd, {'out_io': 'buffer', 'out_buf': bufnr('%')})

Works fine, but when I switch to new buffer, and then return back, created buffer is empty. So, looks like vim doesn’t keep contents of nofile buffers.
Is there any way to keep nofile buffer contents for vim session?