Personally, I view coincidence and synchronicity as synonyms because my favorite dictionary defines coincidence as a “Noteworthy event, circumstance, or series of such, which occurs in conjunction, or synchronously, with others, and is of such a character as to suggest a connection of cause and effect, although apparently no connection of the kind exists.” Thus to me, when only chance is involved, it's happenstance, not coincidence or synchronicity.

Others do distinguish between the terms and say a coincidence is a synchronicity when it has meaning to the observer--others may say it has to be objectively meaningful and not the result of probabilities. In fact, Carl Jung coined the term synchronicity and defined it as a meaningful coincidence.

You might find this piece of mine helpful. https://medium.com/promptly-written/spiritual-prompt-for-the-week-of-april-17th-23rd-34b34b26fd6b and this one interesting about a very specific type of coincidence, the mirror coincidence. https://medium.com/channspirations/mirror-coincidences-41893e2e55ed