We are also seeing this in OpenSUSE OBS (Open Build System) on openSUSE Leap 15.2 with perl 5.26:
https://build.opensuse.org/package/live_build_log/openSUSE:Leap:15.2/perl-Data-Dump-Streamer/standard/x86_64
[ 18s] + ./Build test
[ 19s] t/as.t .............. ok
[ 19s] t/blessed.t ......... ok
[ 19s] t/dogpound.t ........ ok
[ 19s] t/dump.t ............ ok
[ 20s] t/filter.t .......... ok
[ 20s] t/globtest.t ........ ok
[ 20s] t/hardrefs.t ........ ok
[ 20s] t/impure_madness.t .. ok
[ 21s] #
[ 21s] # PadWalker isn't installed
[ 21s] t/lexicals.t ........ ok
[ 21s] t/locked.t .......... ok
[ 21s] t/madness.t ......... ok
[ 21s] t/madness_json.t .... skipped: No JSON::XS
[ 21s] t/madness_w.t ....... ok
[ 22s] t/names.t ........... ok
[ 22s] t/overload.t ........ ok
[ 22s] t/readonly.t ........ ok
[ 22s] t/refaddr.t ......... ok
[ 22s] t/refcount.t ........
[ 22s] Failed 10/18 subtests
[ 23s] t/refelem.t ......... ok
[ 23s] t/reftype.t ......... ok
[ 23s] t/sortkeys.t ........ ok
[ 23s] t/tree.t ............ ok
[ 23s] t/usage.t ........... ok
[ 24s] t/xs_subs.t ......... ok
[ 24s]
[ 24s] Test Summary Report
[ 24s] -------------------
[ 24s] t/refcount.t (Wstat: 11 Tests: 8 Failed: 0)
[ 24s] Non-zero wait status: 11
[ 24s] Parse errors: Bad plan. You planned 18 tests but ran 8.
[ 24s] Files=24, Tests=352, 5 wallclock secs ( 0.16 usr 0.11 sys + 4.34 cusr 0.51 csys = 5.12 CPU)
[ 24s] Result: FAIL
[ 24s] Failed 1/24 test programs. 0/352 subtests failed.