Cannot add column to list and columns disappearing on save

I am having a new and strange issue with CB Lists. I have a list that works fine (it contains 4 columns). Today I am trying to add another column to the list but there are failures and strange results.

I click the Add Columns button and get the usual options. I supply all information and choose the CB field to be used and move the column to the desired position. But when I save it, the newly added column disappears, along with the column that was just below it.

If I do the same process as above but I do not move the newly created column and save it, the new column does not disappear from the list management page but when trying to open the list on the frontend I get the following error:

PHP regular expression limit reached (pcre.backtrack_limit)

I have not installed anything new (other than updating Joomla and CB/CBsubs nightly builds)

CB Version 2.5.0
PHP Version 7.3.21

How many fields are you trying to output on your list and are selected in the columns? I'm not seeing any issues with adding new columns, but see a minor possible error when moving a column. Try adding the column, saving, then moving it and saving.

Columns 1, 2 and 3 each contain a single field. Column 4 contains 4 fields, so the list contains a total or 7 fields and works fine. There are 439 records in the database that this list shows. It is only by trying to add one more field/column that the problems begin.

Adding the column then saving it then moving it and saving it again results in the column disappearing and sometimes the existing column just below also disappears.

My workaround was to add the new list field as a row to one of the already existing columns, rather than as a stand alone column. This strategy did not create any errors. That will work for our purposes, but we have some other lists that we need to make so it will be helpful to understand about the problem of click and drag to move row not working.

Strange, I'm having no issues adding new columns or fields to those columns. Please PM backend super administrator login credentials after creating a test userlist where the problem can be seen an will take a look. It's possible there's a JS error happening that's breaking the repeat usage.

I was making a new test user list and as I was drag and drop moving columns around, they did start disappearing so I was able to replicate it. I will try to set you up with superuser access.

One thing I noticed when creating the test list is that, when drag and drop repositioning the column order, the format of drop down menus was changing. See attached screen shot. The Select Field menu style was going from the white style menu to the rounded grey style. It happened many times, back and forth, as I moved things around. Not sure if it is relevant but thought I would point it out.

Doing some more tests, suddenly a Position drop down has appeared on one of the column settings. Saving the list a 2nd time made this menu go away. See screenshot: