The Eurail planner is only updates occasionally so if there are differences between the planner and the timetable of the national railway you should trust that of  the national railway.

@Al_G I guess you have good information about UK trains on Boxing Day.

Dec 25 is always closed and Dec 26 is usually a very limited service at best.

A lot of the operators haven’t yet published finalised timetables for the 26th however I wouldn’t be expecting much, long distance routes in particular are likely to have no services, some commuter and routes serving airports usually run a skeleton services.

Scotland is different with 25 Dec and 1 Jan being the main holiday days with no services running, they normally run a public holiday service level on Dec 26.

The following page should give details but has few details at present

https://www.nationalrail.co.uk/service_disruptions/228478.aspx

If there is a specific journey you wish to make give details and we can see what options you have.

Interestingly, the fact that there seems to be a normal Monday timetable in the rail planner app does mean that at some point RDG sent that timetable to the European Timetable Centre. It must have been corrected shortly after, since DB, ÖBB etc. don't show that anymore. The rail planner app will probably be corrected with its next update.

It's also a reminder not to use the rail planner app for any planning: its low update frequency makes it unreliable.

There is also an aggravating factor this year that Dec 27 is also a national holiday (in lieu of Xmas day which is a Sunday) so many services will also be limited (probably a Sunday service). Some of those services may very busy with shoppers and people returning home after Xmas visits.