Last week I had the issue that I was not able to create appointments in VoP after upgrading our Domino environment to V12. I could see the following error message on the server console:

28.05.2021 14:50:36 iNotes XSS Security: Invalid Request, unexpected nonce value; with Referer: ‘https://server.company.com/mail/mailfile.nsf/($Calendar)/$new/?OpenDocument&ui=dwa_frame&l=de&gz&CR&MX&TSF=20210422T064359,78Z&TS=20210528T125024,08Z&charset
=UTF-8&charset=UTF-8&KIC&ua=safari&pt&gn&em=1&sq&PresetFields=h_SkinTypeOverride;h_Empty,s_CustomCalCSS;f’. Request not processed, throwing exception.

After clearing the browser cache ( thanks to my friend Milan Matejic ) everything worked fine again.

I opened a case at HCL and received the following informations and hints:

the following entries in the NOTES.INI of the server and a restart of the HTTP server solved this issue:

iNotes_WA_Security_NonceCheck=0
iNotes_WA_Security_RefererCheck=0

Reference Article:
https://support.hcltechsw.com/csm?id=kb_article&sysparm_article=KB0076391
https://support.hcltechsw.com/csm?id=kb_article&sysparm_article=KB0038592

Another setting in the NOTES.INI was mentioned for setting an Automatic Cache Clearing Level:

iNotes_WA_LogoutScrubType

In the following link all possible values are listed: https://ds_infolib.hcltechsw.com/ldd/dominowiki.nsf/dx/Set_the_Automatic_Cache_Clearing_Level_for_the_Lotus_iNotes_server