Something has changed if it was working before. You said it happens on every site you publish are they on the same hosting provider? If so then perhaps there’s been a change at their end.
Have you tried to connect with another FTP application with the same credentials?
You might want to go through the steps outlined in this KB:
It could be the theme, but as many people that are using foundry I would think others would be having the same issue.
Have you tried to publish to a local folder with the problem projects?
If you get the same error then it’s definitely a resource issue.
After that I would try to publish each page (locally) one at a time and isolate the problem.
I remove all pages except one page, try it locally and it is the same thing.
(but I notice that the first time it publish well it is always after that the problem happen)
I try to remove element one by one, republish and it ia the same thing.
Even if I remove everything (blank page) from the page and publish, it does not work!!!
Like I said it happen with another completety different site except for the theme.