こともあって is used to indicate that something is one of the reasons (among possibly others) for a particular result or situation. It translates to "partly because," "also because of," or "in part due to the fact that." The speaker acknowledges the stated reason as a contributing factor without claiming it is the sole cause.
This expression connects a reason clause to a result clause. The reason given before こともあって is presented as one notable factor that led to the outcome described in the main clause.
こともあって attaches to the plain form of verbs, adjectives, and nouns:
Unlike ので or から, which present a reason as the primary or sole cause, こともあって implies that there are other contributing factors as well. The stated reason is simply one that the speaker finds worth mentioning. This makes the expression sound more nuanced and less direct, which is common in formal writing, news articles, and explanatory speech.
The form こともあり is used in the same way and is slightly more formal or literary. Both are interchangeable in most contexts.