Failed link (from Dictionary anomalies)
Working link (from same place, open in new private window)
The two links look identical to my eye (and I would expect them to be, as one wouldn’t expect all browsers to suddenly start corrupting links in the same contexts).
The symptom is that the same links either do or don’t work depending on whether they are opened in same tab, new tab, new window, or new private window. The pages get well drawn before being overwritten by 403/404 error declarations. A hypothesis would be that the scripts are failing to obtain a connection to the relevant database. Presuming that the same database software is being used for both the observations and dictionary the different error codes suggest that they error codes are being generated by either server or client side scripts, most likely the former, rather than by the underlying database or server software.