It's nightmarish. The developer did not modify the invasion product. He was mandated by the parties to identify who is responsible for the problem: site became non-functional after an update. Since this case, specifications have been created to avoid the risk of a total breakdown.
I cannot perform the update since I have error messages in the invision Admin interface which prevents me from finalizing standard maintenance operations.
I modified in PHP 8, it seems that the procedure for cleaning the caches of the website, even if it is not finished, has corrected the phenomenon of the white page.