How to fix an error after installing a new Drupal 8 theme?

Question

PHP

Drupal 8 hosted by SmartAPE.
Developed locally (at home, ubuntu 14.03 apache2 mysql)
Transferred to hosting, installed, configured everything worked fine.
I installed the new theme integrity 8.x-1.6 and got this error Warning: array_flip(): Can only flip STRING and INTEGER values! in Drupal\Core\Entity\EntityStorageBase->loadMultiple() (line 232 of core/lib/Drupal/Core/Entity/EntityStorageBase.php). (repeated five times)
What is the reason for this and how to fix it?
-------------------------------------------------- -------------------------------------------------- -
Added (it seems after disabling slides)
Notice: Undefined offset: 0 in _integrity_get_home_block_contents() (line 89 of themes/integrity/integrity.theme).
Before each (previous) error.