If the project root is not found it can't save the jump points. You can fix this by defining more project roots like
opts = {
open_callback = require("marlin.callbacks").use_split,
patterns = { ".git", ".svn", "Makefile", "Cargo.toml", "." },
},Or disabling the message with (But jump points won't be saved)
opts = {
suppress = {
missing_root = false
}
}