Transcontinental Race No. 8 - TCR8 - #TCRN08 - 2022

I think it's mostly different variations of exactly that.
At the extreme end it's doing a bit of motorway. Usually it's nothing like the M1, but maybe a short bit joining two OK roads, or a quiet motorway with a hard shoulder that all the locals use to cycle on because its actually better (and probably safer) than the other roads, or going the wrong way down a slip road to miss out a big junction. Or it could be a 'car only' A road, which are common in Germany, Hungary and elsewhere. Or a road where cycling is allowed but which the race has banned. This might be specific tunnels, or E roads in Romania, etc.
It could also be missing out a bit of parcours.
I can't think off the top of my head any other common reasons people get penalties.

These are the reasons for penalties mentioned in the 2019 results

The penalties awarded to riders reflect the following:

1. Errors in effective route planning.

2. Failure to correct a routing error promptly.

3. Penalties for rule infringements.

Significant rule infringements (particularly where rider safety is
compromised) and failure to correct promptly and in a safe manner
could mean exclusion from the race results.

Looking at the results from the last two races I was in, both of them had a rider disqualified because of riding on a motorway and also one for riding without a helmet and a light at night.

I dotwatched too in 2018 and at least one thing in addition to just checking the route was going through the social media, to check if the racers ask for help or if they have their own photographers without asking for permission and a media license. Or if they ride together with someone else for a longer time, stopping for a break and leaving again together.