My experience is that these are usually caused by bad-quality frontend code that does not properly handle errors around bad-quality analytics SDKs, and breaks in subtle ways when these SDKs throw exceptions.
The e-commerce industry is obsessed with tracking and optimizing their conversion rate, so a lot of them have a lot of manual instrumentation of their "user journeys". Imagine they emit an analytic event after you fill your address, and before unlocking the next checkout step. If uBO blocks the analytics event submission and the SDK throws an exception, that next checkout step won't unlock unless they implemented basic error handling.
