has anybody had to use a "sliding window" in industry outside of leetcode?

I have seen a "sliding window average" being used as signal filter for measurement values. That's a simple low-pass filter to reduce transient noise.

I've had to use sliding window in real-time analytics of sensor data.

Caches

Caches, low pass filters, anomaly detection, ML on sequential data (including images), derivatives on general which are a common part of any analysis job or anything to do with a streaming sensor, this could even be low level mouse handling in games.

Sliding window as in SQL aggregate functions?

Also, indexing for full text search.

Compression algos

Not recently. But i definitely needed one for n-gram histogram generation in a crawler project. Probably used them for other things too, but can't remember. Never tried leetcode though.

Circuit breakers in Resilience4J