bumping up to urgent, as apparently the crashes dump the client at times (but not every time).

well, on demo I created two moves to simulate the problem :

Company,Number,Journal,Period,Effective Date,Description,State (string),Lines/Account,Lines/Debit,Lines/Credit
Michael Scott Paper Company,7,Bank,2021-09,09/22/2021,pong,Draft,Main Payable,100,
,,,,,,,Main Cash,0,100
Michael Scott Paper Company,15,Expense,2021-09,09/01/2021,ping,Draft,Main Payable,,100
,,,,,,,Main Expense,100,0

then went to charts->open chart of accounts and opened 'Main payable'

Then entered a filter: "Reconciliation: ="
then reconciled 'ping' with 'pong'
then refreshed.... pow

you may have to create new moves

Please provide a scenario to replicate the error.

with tryton-6.0.6, after reconciling some moves directly via the accounting plan, if I refresh, I get the following error:

ERROR:tryton.common.common:  File "/usr/lib/python3.9/site-packages/tryton/gui/window/view_form/view/list.py", line 1005, in __select_changed
    if not previous_record.validate(self.get_fields()):
  File "/usr/lib/python3.9/site-packages/tryton/gui/window/view_form/model/record.py", line 390, in validate
    self._check_load(fields)
  File "/usr/lib/python3.9/site-packages/tryton/gui/window/view_form/model/record.py", line 251, in _check_load
    self.reload(fields)
  File "/usr/lib/python3.9/site-packages/tryton/gui/window/view_form/model/record.py", line 495, in reload
    self.validate(fields or [])
  File "/usr/lib/python3.9/site-packages/tryton/gui/window/view_form/model/record.py", line 390, in validate
    self._check_load(fields)
  File "/usr/lib/python3.9/site-packages/tryton/gui/window/view_form/model/record.py", line 251, in _check_load
    self.reload(fields)
  File "/usr/lib/python3.9/site-packages/tryton/gui/window/view_form/model/record.py", line 495, in reload
    self.validate(fields or [])
  File "/usr/lib/python3.9/site-packages/tryton/gui/window/view_form/model/record.py", line 390, in validate
    self._check_load(fields)
  File "/usr/lib/python3.9/site-packages/tryton/gui/window/view_form/model/record.py", line 251, in _check_load
    self.reload(fields)
  File "/usr/lib/python3.9/site-packages/tryton/gui/window/view_form/model/record.py", line 495, in reload
    self.validate(fields or [])
  File "/usr/lib/python3.9/site-packages/tryton/gui/window/view_form/model/record.py", line 390, in validate
    self._check_load(fields)
  File "/usr/lib/python3.9/site-packages/tryton/gui/window/view_form/model/record.py", line 251, in _check_load
    self.reload(fields)
  File "/usr/lib/python3.9/site-packages/tryton/gui/window/view_form/model/record.py", line 495, in reload
    self.validate(fields or [])
... [repeated many times]
 File "/usr/lib/python3.9/site-packages/tryton/gui/window/view_form/model/record.py", line 390, in validate
    self._check_load(fields)
  File "/usr/lib/python3.9/site-packages/tryton/gui/window/view_form/model/record.py", line 250, in _check_load
    if not self.get_loaded(fields):
  File "/usr/lib/python3.9/site-packages/tryton/gui/window/view_form/model/record.py", line 261, in get_loaded
    return set(fields) <= (self._loaded | set(self.modified_fields))

RecursionError: maximum recursion depth exceeded in comparison

(tryton:3748): Gdk-WARNING **: 09:30:12.720: The program 'tryton' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadAlloc (insufficient resources for operation)'.
  (Details: serial 133467 error_code 11 request_code 130 (MIT-SHM) minor_code 5)
  (Note to programmers: normally, X errors are reported asynchronously;
   that is, you will receive the error a while after causing it.
   To debug your program, run it with the GDK_SYNCHRONIZE environment
   variable to change this behavior. You can then get a meaningful
   backtrace from your debugger if you break on the gdk_x_error() function.)

as it has happened a few times it seems repeatable.