Empty selections after adding indexes on a pivot table. Why?

Question

Laravel

Added in migrations:
Schema::table('author_book', function (Blueprint $table) {
$table->foreign('book_id')->references('id')->on('books')->onDelete( 'cascade');
$table->foreign('author_id')->references('id')->on('authors')->onDelete('cascade');
});
From a curious, raw sql query (peeped in telescope) gets the data. But laravel itself began to return an empty result in all places where a pivot table is used. The point is in the indexes, since it was worth deleting them in SequelPro, so everything became normal again.