After some template renaming mystery happens – twig looking for wrong template and did not find it even it really exists:
Unable to find template "form/bootstrap_3_horizontal_layout.html.twig" (looked into: /home/travel/www/gai/app/Resources/views, /home/travel/www/gai/vendor/symfony/symfony/src/Symfony/Bridge/Twig/Resources/views/Form).
Symfony debugger points to error at line 31:
30 {% form_theme edit_form 'form/bootstrap_3_horizontal_numbers.html.twig' %}
31 {{ form_start(edit_form) }}
32 <div class="box-body">
33 {{ form_widget(edit_form) }}
34 </div>
However as you may notice it fails to find theme *layout.html.twig not the *numbers.html.twig.
You may say it may be some issue with caching? It may be but I cleared it as well as know how to: php bin/console cache:clear, rm -rf app/cache. Will be appreciate ideas about what I'm missing. Thank you.
EDIT:
Here is output of ls -la app/Resources/views/form/
drwxrwxr-x 2 travel travel 4096 Geg 3 08:56 .
drwxrwxr-x 11 travel travel 4096 Bal 23 23:47 ..
-rw-rw-r-- 1 travel travel 2399 Geg 3 08:56 bootstrap_3_horizontal_layout.html
-rw-rw-r-- 1 travel travel 2577 Geg 3 00:22 bootstrap_3_horizontal_numbers.html.twig
-rw-rw-r-- 1 travel travel 9668 Kov 19 10:20 bootstrap_3_layout.html.twig
After reading the output of ls -la the most obviously reason should be that your *layout.html file is missing the .twig ending in the filename.
Error message:
Unable to find template "form/bootstrap_3_horizontal_layout.html.twig"
Filename:
form/bootstrap_3_horizontal_layout.html
Change Filename to:
form/bootstrap_3_horizontal_layout.html.twig
You have probably renamed the symfony twig file by accident (if using safe refactoring on phpstorm or something) and now that original file could not be found because it's name is changed. You should locate that file and changed it name back to the original and try again.