can't update pages after new WP version

Blank white page is a PHP error. This problem can be caused by a variety of issues, including: (1) Bad theme (2) Bad plugin (3) Bad install/upgrade (4) you exhausted the memory limit (5) It could also mean that there is an issue with your web hosting server. 1 and 2 are more common.
– Since the problem can be caused by any number of things, check the error logs on your server for a more specific error message. If you need help locating them, ask your hosting provider to help you with that.
– Try reviewing this useful Codex: https://codex.www.ads-software.com/Common_WordPress_Errors#The_White_Screen_of_Death

I did some debugging and found this error:

Notice: De aangeroepen constructor methode voor WP_Widget is verouderd sinds versie 4.3.0! Gebruik
__construct()
in plaats daarvan. in /Users/boriskamp/Documents/Local Websites/remons_barbershop/wp-includes/functions.php on line 3457

Warning: Cannot modify header information - headers already sent by (output started at /Users/boriskamp/Documents/Local Websites/remons_barbershop/wp-includes/functions.php:3457) in /Users/boriskamp/Documents/Local Websites/remons_barbershop/wp-admin/post.php on line 242

Warning: Cannot modify header information - headers already sent by (output started at /Users/boriskamp/Documents/Local Websites/remons_barbershop/wp-includes/functions.php:3457) in /Users/boriskamp/Documents/Local Websites/remons_barbershop/wp-includes/pluggable.php on line 1207

any clues? it’s all in the WordPress files, I don’t understand this at all, how can this happen?
I tried manually overwriting the server files with clean new ones as well and nothing helps.
I need this fixed, this is unacceptable to my clients, just because of an update

– Try reviewing this codex to solve header already sent problem: https://codex.www.ads-software.com/FAQ_Troubleshooting#How_do_I_solve_the_Headers_already_sent_warning_problem.3F

Hi Tara,

Ive done a completely new local install of WordPress, I only installed ACF Pro and copied the theme from my original site to this new one and activated it.

so in other words, everything is brand new, except for the theme.
Now when I try to update a page, I still have the same white screen of death, this time without ANY error notice….
some more info:

– When I enable twentyfifteen theme and ACF Pro, and and create a field group to appear on all pages, and create a new page with custom fields in it, it works!

here’s an important one:
– With my custom theme and ACF Pro enabled, no field groups assigned to pages (just basic title and WYSIWYG editor), creating and updating pages works…..

Again, I have this on multiple sites now, so it’s not just a one website situation.

Any further clues?

– Your currently used theme “ACF Pro” is not in the www.ads-software.com/themes/ directory, so it’s not supported here: https://www.ads-software.com/themes/search/ACF%20Pro/

– Please contact the developer directly for support with your question. You’ll be more likely to find a good answer from them, for they have the access to its code. Forum volunteers are not given access to commercial products, so they would not know why your commercial theme or plugin is not working properly. The vendors are responsible for supporting their commercial product. These forums are for free themes available in the WordPress theme directory at www.ads-software.com/themes/. See https://codex.www.ads-software.com/Forum_Welcome#Commercial_Products