Sometimes really slow 'make check' in pipeline

Maybe a /dev/random related delay? Canceling a job gives a backtrace like this:

Terminated
FAIL: tests/x509-auth.scm
======================================================
   Guile-GnuTLS 4.0.0.18-b2b0: guile/test-suite.log
======================================================
# TOTAL: 23
# PASS:  22
# SKIP:  0
# XFAIL: 0
# FAIL:  1
# XPASS: 0
# ERROR: 0
.. contents:: :depth: 2
FAIL: tests/x509-auth.scm
=========================
throw to `gnutls-error' with args (#<gnutls-error-enum Public key signing has failed.> handshake) [PID 14806]
          14 (primitive-load "/builds/gnutls/guile/guile/./tests/x50?")
In ice-9/eval.scm:
    155:9 13 (_ _)
In ice-9/boot-9.scm:
  1731:15 12 (with-exception-handler #<procedure 5794537996f0 at ic?> ?)
  1736:10 11 (with-exception-handler _ _ #:unwind? _ # _)
    142:2 10 (dynamic-wind _ _ #<procedure 5794537ac4c0 at ice-9/eva?>)
In ice-9/eval.scm:
    155:9  9 (_ _)
   279:15  8 (_ #(#(#<directory (gnutls build tests) 5794535755a0> ?)))
    619:8  7 (_ #(#(#(#<directory (guile-user) 579453575f00> # ?)) ?))
In unknown file:
           6 (handshake #<session 5794537b6fe0>)
In ice-9/boot-9.scm:
  1669:16  5 (raise-exception _ #:continuable? _)
  1764:13  4 (_ #<&compound-exception components: (#<&error> #<&irri?>)
In ice-9/eval.scm:
    619:8  3 (_ #(#(#<directory (gnutls build tests) 5794535755a0>) ?))
In ice-9/boot-9.scm:
    142:2  2 (dynamic-wind #<procedure 5794537b1b80 at ice-9/eval.s?> ?)
In ice-9/eval.scm:
    159:9  1 (_ #(#(#<directory (gnutls build tests) 5794535755a0> ?)))
In unknown file:
           0 (make-stack #t)
FAIL tests/x509-auth.scm (exit status: 143)