I managed to get this reproduced [1]. A first JMC analysis indicates this seems to be related to the revised data structures for main-memory updates [2]. A small overhead would be expectable and acceptable, but definitely not on this scale. Thanks for the observation.
[1] https://github.com/BaseXdb/basex/issues/2134 [2] https://docs.basex.org/wiki/BaseX_10#Main-Memory_Updates
