From screenshot:

"exception during generator call: TypeError:
'NoneType' object is not callable"

A google search shows that this issue had similar error reports:
   https://github.com/LinuxCNC/linuxcnc/issues/217

Issue 217 was reportedly fixed by merge of pull221:
   https://github.com/LinuxCNC/linuxcnc/pull/221

by commit: 3b5c5d99d:
   https://github.com/LinuxCNC/linuxcnc/pull/221/commits/3b5c5d99d937e7d17e4593c22b40b2dea6bef70f

This commit is in master but not in 2.7
I think your 2.8 config is finding a 2.7 version of stdglue.py
which is likely not compatible.

#--------------------------------------------------------------
Your 2.8 ini file has uses a remap and has:
[PYTHON]
TOPLEVEL=./toplevel.py
PATH_APPEND= ./
### PATH_APPEND= ../../nc_files/remap_lib/python-stdglue/
###PATH_APPEND= /home/tom/linuxcnc/nc_files/remap_lib/python-stdglue/
PATH_APPEND= ../../nc_files/remap_lib/python-stdglue/

Your remap.py file says: "from stdglue import *" so it
requires stdglue.py and will find it using [PYTHON]PATH_APPEND
as:
     ../../nc_files/remap_lib/python-stdglue/stdglue.py

#--------------------------------------------------------------
Looking at the ls -lR report (list.txt):

/home/tom/linuxcnc/nc_files/remap_lib/python-stdglue:
total 28
-rw-r--r-- 1 tom tom 14913 Jul 29  2017 stdglue.py

From the file size (14913) i note that this is a 2.7 version
of stdglue.py which is not compatible for 2.8 after the commit
above (i think, a brief test confirmed).

#--------------------------------------------------------------
Users often start by using the linuxcnc configuration
picker.  When configurations are created by the
configuration picker, the ~/linuxcnc/nc_files/ directory
includes symbolic links for the *_lib directories that point
to system directories that are installed with the linuxcnc
deb.  Example:

$ ls -gGlR ~/linuxcnc/nc_files
/home/dgarrett/linuxcnc/nc_files:
total 4
lrwxrwxrwx 1   27 Feb  8 11:38 examples -> /usr/share/linuxcnc/ncfiles
lrwxrwxrwx 1   36 Feb  8 11:38 gcmc_lib -> /usr/share/linuxcnc/ncfiles/gcmc_lib
lrwxrwxrwx 1   40 Feb  8 11:38 gladevcp_lib -> /usr/share/linuxcnc/ncfiles/gladevcp_lib
lrwxrwxrwx 1   38 Feb  8 11:38 ngcgui_lib -> /usr/share/linuxcnc/ncfiles/ngcgui_lib
-rw-r--r-- 1 1542 Feb  8 11:38 readme.ngc
lrwxrwxrwx 1   37 Feb  8 11:38 remap_lib -> /usr/share/linuxcnc/ncfiles/remap_lib

With these links, all the *_lib/* files are updated when a
new linuxcnc deb is installed.

In your case, the directory:

   /home/tom/linuxcnc/nc_files/remap_lib

(and similar *_lib dirs) is not a symbolic link but an
actual directory that includes copies of system files from
2.7.   There is nothing wrong with this but it means you do
not benefit from updates to system files in:

   /usr/share/linuxcnc/ncfiles/remap_lib/

when installing an updated linuxcnc deb.

#--------------------------------------------------------------
There are numerous ways to address this:

1) you could copy the system:
       /usr/share/linuxcnc/ncfiles/remap_lib/
   directories and all sub directories and files from the
   2.8 deb installation to your local directory:

       /home/tom/nc_files/remap_lib/

   and maintain them there if you *don't* want automatic
   system updates.

2) you could implement symbolic links to benefit from system updates
   similar to the way the configuration picker does it:
   For example:

   # first save your local directory:
   mv /home/tom/linuxcnc/nc_files/remap_lib /home/tom/linuxcnc/nc_files/SAVE_remap_lib

   # then make the symbolic link:
   ln -s /usr/share/linuxcnc/ncfiles/remap_lib /home/tom/linuxcnc/nc_files/remap_lib

3) you could make your ini file setting point to the system
   directory:
   [PYTHON]
   PATH_APPEND = /usr/share/linuxcnc/ncfiles/remap_lib/python-stdglue/

4) numerous other ways

#--------------------------------------------------------------
I know this is all complicated but there are many ways to
configure and the flexibility is used by folks that want
to create or customize their own special *_lib/ files.

If you always want to use system files, i think the method 2
above is fairly safe.

Notes:
1) i could be wrong about all of this as i have never used remaps
2) the author of all the remap stuff no longer contributes to
   either LinuxCNC or Machinekit so it can be a problem
   when stuff happens
2) there may be other problems after stdglue is fixed
3) using local copies of the other *_lib directories means
   the same liabilities exist if system deb updates changes
   *_lib files
   I see you do have a link for the nc_files/examples:
     /home/tom/linuxcnc/nc_files/examples -> /usr/share/linuxcnc/examples
   but no links for remap_lib, ngcgui_lib, gcmc_lib, gladevcp_lib
4) notes above apply to deb installs, using a RIP build
   is very different with regards to location of files
5) beware, i often make typos in all the typing above


# 190320:08.11