'A couple' can take a singular or plural verb

Appearing in an online newspaper report is the sentence, "A couple who was reconciling their marriage was found dead in a hotel room."

'Couple' here is referring to two people, and like many other collective nouns, it may take either a singular or a plural verb though most commonly, it is construed as a plural.

The sentence in italics is taking it as a singular which is, however, not in harmony with the word 'reconciling' and the plural pronoun 'their'.

To be grammatically correct, the sentence needs to be recast as "A couple who were reconciling their marriage were found dead in a hotel room."