To display the number of submissions for each Community, change value of "webui.strengths.show" from "false" to "true" in dspace.cfg as show below:
Note: By default, an index count will be performed in real time when pages are loaded. If you wish to prevent this, uncomment "webui.strengths.cache = true" and set the value to "false"
# Whether to display collection and community strengths (i.e. item counts)
# XMLUI only makes strengths available to themes if this is set to true!
# To show strengths in the XMLUI, you also need to create or use a theme which
# displays them.
webui.strengths.show = true
# if showing strengths, should they be counted in real time or
# fetched from cache?
# Counts fetched in real time will perform an actual count of the
# index contents every time a page with this feature is requested,
# which may not scale as well as a cached count.
# The default behaviour is to use a cache.
# webui.strengths.cache = true