Yes, if you were using a unified numeration, that would be an issue. But in this case there is a unique aspect to it that would provide autonomy. One caveat to this though, the proposed solution is based on user initials, one could surmise that there is a very real potential that there are two users with the same initials - in which case I would say something more unique to that user would be needed rather than initials.
But back to your point, I still don't believe that would be a concern - the onvisible and until saved aspect - because the only thing that is calculated in the variable is the "LOG-xx" (xx is user initials). The actual sequence number based on that is determined in the Default property of the datacard for a New record. The variable never changes nor needs to change, it is only put into its own separate calculation so that it is not in the Filter function - in which case PowerApps will evaluate it during the filter and trigger a delegation issue.
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