Jumbled letters in emails

a small number of subscribers are receiving emails with jumbled letters for words that make no sense and cannot be read. Started after update to
using latest vs phplist 3-6-8 (reinstalled twice)
mysql 5
php 7.4 cgi
php cli 8.0

the jumbled email e.g. a mixture of message and coding) or simply no content at all when an email is sent.