icalender self deleting information from created events since Big Sur Update

Hi does any one have the same issue or do they know how to fix the following as apple have been working on this issue for the last 5 months and cant fix it (it started after I upgraded to Big Sur.

basically I create new events on icalendar to share with staff members (image no: 1), but I keep losing the information, when I change the event to a different calendar, unless I am very quick and I copy and paste the event, this then puts 2 copies on the calendar app, but one deletes the extra information and one holds on to the info. please see images to explain

I have multiple calendars set up for example

1: new event (Purple)

2: Engineer No2: (Red)

3: Engineer No3: (Blue)

(image no: 1) created a new event - all works fine

(image no: 2) add additional text info to the event to explain more details.

(image no: 3) change the calendar from new event to "Ollies" Calendar, then within a few seconds the "modified test is erased". shown in image no 4:

(image no: 4), The event created has reverted back to the original event with original text, but colour has stayed the same to what I changed it to. We only lose the modified text), however if if I cut and paste the event as in image 3) then I can keep the info in one of the 2 events created see image no 5.

(image no: 5) new event had the text modified then I changed the calender from new event to ollie , then cut and posted the event, shown below, but then after a few seconds the copied event deletes the modified text in one of the events created. I can then deleted the whole event and keep the copied event and all is ok,

but this is really annoying, and apple cant seem to fix the issue. after 5 months im now thinking of sharing some other calendar app with my staff as this has been a nightmare. ive been using I calender for over 10 years and its been fine until the Big Sur update. ca any one please advise what I can do.

this happens across all our 5 computers all on the same Icloud account, we have even created a new iCloud account and it does exactly the same thing.

if we create events directly on icoud web based calendar then its fine, its only when we modify using the icalendter app on the computers.

hope this explains so any one can understand and hopefully help.