I've have repeated and consistent failures downloading reports.
For example, if I attempt to print just eight records in a combined Word document it always fails to produce all eight, I'd get maybe 2 or 3. To its credit, the app does clearly report the IDs of those that fail, so I just filter for those and try again. Of the remaining set, some will work and others not. Persistence pays and eventually all are printed. I then spend more time combining them. What should be a few minutes takes hours, and for a AEC consultancy that is a show stopper right there.
We chose not to use Survey123 reports for an airport pavement inspection survey and ground remediation survey because of the unreliability and inefficiency of the reporting service (and one that charges a cost premium in credits). The pavement inspection survey had more than 2k records and I'm not going to request those reports in groups of 2 and 3 just to make it work. Instead, we're using a mix of Pro map series with dynamic data, formatted Excel spreadsheets and mail-merge reports driven by the XLS. It requires a simpler survey design but is a reliable way to get a formatted report out of Survey123
I think the idea of Survey123 reports is brilliant. But I would only consider using it when it has the reliability of ArcGIS Online, when it always works and can export a few hundred, if not a few thousand surveys into a combined document without errors.