Saw https://github.com/freebsd/poudriere/issues/917 and confirm symptoms described there. 

While I tried to rerun bulk runs I noticed that the swapspace is not used at all. Likely this prevents allocation of sufficient memory space.

My related  poudriere.conf settings:

# When building packages, a memory device can be used to speedup the build.
# Only one of MFSSIZE or USE_TMPFS is supported. TMPFS is generally faster
# and will expand to the needed amount of RAM. MFS is a slower since it
# uses UFS and several abstraction layers.

# If set WRKDIRPREFIX will be mdmfs of the given size (mM or gG)
#MFSSIZE=4G

# Use tmpfs(5)
# This can be a space-separated list of options:
# wrkdir    - Use tmpfs(5) for port building WRKDIRPREFIX
# data      - Use tmpfs(5) for poudriere cache/temp build data
# localbase - Use tmpfs(5) for LOCALBASE (installing ports for packaging/testing)
# all       - Run the entire build in memory, including builder jails.
# yes       - Enables tmpfs(5) for wrkdir and data
# no        - Disable use of tmpfs(5)
# EXAMPLE: USE_TMPFS="wrkdir data"
USE_TMPFS=no

# How much memory to limit tmpfs size to for *each builder* in GiB
# (default: none)
#TMPFS_LIMIT=8

# How much memory to limit jail processes to for *each builder*
# in GiB (default: none)
#MAX_MEMORY=8