G1 remark long pause doing reference processing

Issue

• A G1 remark is taking a very long time, much longer than the sum of SoftReference + WeakReference + FinalReference + PhantomReference + JNI Weak Reference processing:

2021-08-20T11:53:44.348+0100:   2377830.399: [GC remark 
    2021-08-20T11:53:44.348+0100:   2377830.399: [Finalize Marking, 0.0012914 secs] 
    2021-08-20T11:53:44.350+0100:   2377830.400: [GC ref-proc
        2021-08-20T11:53:44.350+0100:   2377830.400: [SoftReference, 18076174 refs, 2.6283514 secs]
        2021-08-20T11:53:46.978+0100:   2377833.028: [WeakReference, 18636 refs, 0.0029750 secs]
        2021-08-20T11:53:46.981+0100:   2377833.031: [FinalReference, 17387271 refs, 2.5263032 secs]
        2021-08-20T11:53:49.507+0100:   2377835.558: [PhantomReference, 0 refs, 2136 refs, 0.0012040 secs]
        2021-08-20T11:53:49.509+0100:   2377835.559: [JNI Weak Reference, 0.0001679 secs], 14.8775199 secs] 
2021-08-20T11:53:59.227+0100:   2377845.278: [Unloading, 0.0178265 secs], 14.9383332 secs]
[Times: user=87.40 sys=7.95, real=14.94 secs]