As someone who used to be in construction, painting and landscaping are the last things done.
This is a hit job.
What probably happened is a portion of the paint work didn’t meet expectations or was the wrong color.
They are withholding payment until job is done correctly.
Not only that, but if the project was only completed in June, it seems pretty early to have filed a lien for non-payment. Commercial invoices are rarely past due in such a short time. More likely, some of these contractors filed liens just as leverage to get paid promptly and they aren’t even past due yet.