In general there is a limit in adding widgets at once on PHP level. In most cases there’s enough space to add a lot of widgets, but at some point there is a specific problem of sending data.
By the way, this is a common issue in WP, and it exists also in the Menus area.
To solve this issue there are 2 options:
1. If you have access to the php.ini file on your server – you can insert the following code: max_input_vars = 5000
2. Request from the web host to increase the value of data saving in PHP to what I wrote in the previous solution.
You can always try to minimize the use of widgets and rows in the Page Builder to its minimum and it will work ok.