How to solve page--front.tpl.php page cache problem in drupal 7?

Question

PHP

The situation is this, there is a template for the main page of the site page--front.tpl.php.
Made 1 harmless change
<?php print $messages; ?>
and saved. I go to the main page - there is complete chaos, the layout has flown, everything is displayed incorrectly, etc., I go to other pages - everything is fine.
On other pages you get an error saying I can't load page--front.tpl.php:

Warning: include(/var/www/html/sites/all/themes/mytheme/templates/page--front.tpl.php) [function.include]: failed to open stream: Permission denied в функции theme_render_template() (строка 1505 в файле var/www/html/includes/theme.inc).

Warning: include() [function.include]: Failed opening '/var/www/html/sites/all/themes/mytheme/templates/page--front.tpl.php' for inclusion (include_path='.:/usr/share/pear:/usr/share/php') в функции theme_render_template() (строка 1505 в файле /var/www/html/includes/theme.inc).

I tried to delete the added line - it didn’t help, I also tried the standard methods:
Reset the cache in /admin/config/development/performance
Remove and put back the theme rebuild in /admin/appearance/settings/mytheme
Reset the cache by going to /update.php
Nothing It didn't work, I don't know what else to do.
Before that everything worked great.
Maybe the problem is not in the cache?
Drupal version 7.22
My theme is based on the Zen 5.x theme
UPD #1:
I did all the steps again, for the 4th time everything worked by itself %)
UPD #2:
After the next change in the template, everything started all over again, because of which this does not happen I see.

Answer 1

The problem was solved by setting the permissions to 644 on the page--front.tpl.php file, which was never required before.