Learn Spanish (Latin America): El dron tuvo un cortocircuito, y eso que nunca llovió. - The drone had a short circuit, even though it never rained.

Unlike aunque, which can take the subjunctive when talking about hypotheticals or unverified information, y eso que is used specifically to introduce established statements of fact. Because the speaker knows for sure that it didn't rain, y eso que strictly requires the indicative (llovió).

Could I just say aunque nunca llovió instead? What does y eso que add?

You absolutely could use aunque, but y eso que adds a much stronger sense of surprise, irony, or complaint. It is highly conversational, much like saying "and to think that it never rained!" or "despite the fact it didn't even rain." It heavily emphasizes how unexpected the short circuit was given the conditions.

Why use the preterite tuvo instead of the imperfect tenía for "The drone had..."?

We use the preterite tuvo because the short circuit is being treated as a specific, sudden event that happened and concluded. If you used tenía, it would sound like a background description, as if the drone was just continually existing in a state of having a short circuit over an undefined period.

Is cortocircuito always written as one word?