Heaps are often used as Priority Queues, but what isn't guaranteed in their behavior?

$-$The Heap doesn't completely maintain priority order. Since insertion is always at the bottom, it might

take a while for an high priority item to reach the top

$-$The Heap might not actually maintain First$-$in$,$ First$-$Out order since it is more concerned with priority

value. Two items of identical priority might not resolve in FIFO order

$-$The Heap can only be implemented with an array and will always struggle with memory usage

$-$The Heap might not actually maintain Last$-$in$,$ First$-$Out order since it is more concerned with priority

value. Two items of identical priority might not resolve in LIFO order