On line 248 of /admin/class-equal-height-columns-admin.php the code below will break under PHP 7.2 if the value passed to count isn’t countable.

$field_count = count( $this->options[ $this->options_group_slug ] ) ? count( $this->options[ $this->options_group_slug ] ) : 1;

It should instead also include a call to is_countable()

$field_count = is_countable( $this->options[ $this->options_group_slug ] ) && count( $this->options[ $this->options_group_slug ] ) ? count( $this->options[ $this->options_group_slug ] ) : 1;

Unfortunately is_countable() won’t be added until PHP 7.3 but there’s a really simple polyfill available:
https://github.com/Ayesh/is_countable-polyfill/blob/master/src/is_countable.php