Welcome aboard!!!

To answer your question, this is probably due to "chain stretch" and/or a worn chainring. To check chain wear, measure the distance from pin to pin between ~12 inches of chain. If there is more than a 1/16" of extra length over the 12 inches, then you chain needs replace. Someone else here could probably describe this technique better.

If the chain has stretched too much, more than likely it has also worn the chainring down, and that will need to be replaced also.