why is system getting stuck ...

Recently, I have begun to have recurring issues
with my Linux Mint 18.1 system seeming to get "stuck"
and I can't figure out why. I leave my system running
24/7 and have rarely had a reason or need to shut down.
It has now been running (mostly fine) for 10 days.

The recent problems have happened with both the chrome
browser and the firefox browser (open at separate times).

Various symptoms include the screen seeming to "freeze"
sometimes with the cursor pointer disappearing, sometimes
it changes to an "I" instead of an arrow pointer and is
either unmovable on the screen or sometimes it can be
moved, but at a drunken snail's pace.

Sometimes the screen goes blank and if I walk away and
come back after several minutes, the screen is restored
and the cursor can be moved again.

I have uploaded a screen shot and two text files as
examples, including top.txt ... ps-ef.txt ... and a couple
of screen shots. Can someone tell me what processes ps-ef
show that should be or could be killed?

Why does top-txt show two instances of chrome running ??
Why does top whoc 4 users when 'who' shows only 3?
And why are there 3 users when I am the only user?

http://www.upquick.com/temp/freeze.jpg
http://www.upquick.com/temp/top-txt
http://www.upquick.com/temp/ps-ef.txt

t420: who
joe      tty8         2018-02-28 14:39 (:0)
joe      pts/2        2018-05-22 15:43 (:0)
joe      pts/5        2018-02-28 14:40 (:0)

top - 15:47:20 up 170 days, 5:29, 4 users, load average: 0.22, 1.01,
10.65
Tasks: 245 total, 2 running, 235 sleeping, 0 stopped, 8 zombie
%Cpu(s): 5.0 us, 1.3 sy, 0.0 ni, 93.6 id, 0.1 wa, 0.0 hi, 0.0 si,
0.0 st
KiB Mem: 8056428 total, 3870692 used, 4185736 free, 134676 buffers
KiB Swap: 1951740 total, 1769720 used, 182020 free. 1161048 cached Mem

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
10665 joe       20   0 3832944 239268  63624 S  11.9  3.0   6649:51
plasma-desk+
15697 joe       20   0  511896  50588  35968 S   5.3  0.6   0:05.17 konsole
10241 root      20   0  419892 148588  99172 S   4.0  1.8   1567:26 Xorg
10659 joe       20   0 3247440  90844  18280 S   0.7  1.1 642:54.34 kwin
18274 joe       20   0 1841712 181908     16 S   0.7  2.3  50:10.02
chrome ***** (1)
    8 root      20   0       0      0      0 S   0.3  0.0  75:00.93 rcuos/0
  487 root     -51   0       0      0      0 S   0.3  0.0 464:58.53
irq/44-iwlw+
 1174 root      20   0    4388    224    100 S   0.3  0.0 112:21.59 acpid
14574 root      20   0       0      0      0 S   0.3  0.0   0:00.42
kworker/u16+
15757 joe       20   0   24964   3168   2568 R   0.3  0.0   0:00.81 top
31023 joe       20   0 1752576  36352      0 S   0.3  0.5 149:49.69
chrome ***** (2)
    1 root      20   0   37500   2096      0 S   0.0  0.0   0:14.22 init
    2 root      20   0       0      0      0 S   0.0  0.0   0:03.73 kthreadd
    3 root      20   0       0      0      0 S   0.0  0.0  10:32.60
ksoftirqd/0
    5 root       0 -20       0      0      0 S   0.0  0.0   0:00.00
kworker/0:0H
    7 root      20   0       0      0      0 S   0.0  0.0 136:59.67
rcu_sched
    9 root      20   0       0      0      0 S   0.0  0.0  23:30.73 rcuos/1
   10 root      20   0       0      0      0 S   0.0  0.0  44:27.97 rcuos/2
   11 root      20   0       0      0      0 S   0.0  0.0  25:53.54 rcuos/3
   12 root      20   0       0      0      0 S   0.0  0.0   0:00.01 rcuos/4
   13 root      20   0       0      0      0 S   0.0  0.0   0:00.01 rcuos/5
   14 root      20   0       0      0      0 S   0.0  0.0   0:00.01 rcuos/6
   15 root      20   0       0      0      0 S   0.0  0.0   0:00.01 rcuos/7
   16 root      20   0       0      0      0 S   0.0  0.0   0:00.00 rcu_bh

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