duplicator build cache not clearing

I’ve recently started using the Duplicator plugin and like most other users, rated it at 5. I have encountered a minor anomaly however and would appreciate any advice as all the usual searches have not shed any light. In brief, the clear build cache function doesn’t work and this seems to be because the files are ending up on /public_html/wp-snapshots rather than /public_html/wp-snapshots/tmp. I can delete them manually so its not a major problem, butI wonder whether I’m doing something wrong
Perhaps it’s relevant that in settings the storage path is given as /public_html/wp-snapshots,whereas the clear build cache path is given as /public_html/wp-snapshots/tmp, but I can’t see that they can be changed. The directory permissions for both wp-snapshots and /tmp are set at 755
Thanks