User Credits not being deducted sometimes

We are using ABPro 4.0.3.RC1 to handle vacation request (paid time off).
We use User Credits.
We give everyone a credit balance to draw from based on how much vacation time they get each year.
When someone books a resource, we subtract time from their user credit account (8 hours for a full day or 4 hours for a half day)

For some reason that I can't figure out, sometimes, someone books a resource (for example Full Day that costs 8 hours) the transaction is not being written to the user credit table j3_sv_apptpro3_user_credit_activity and the j3_sv_apptpro3_user_credit table is not being updated. if I cancel the request and re-enter it, it works.

The resource is being booked and the update is being pushed to the google calendar, but the user credit table isn't always being updated.

We have been using this for 4 years at this point and the problem started to occur in December 2018.

Any ideas what I can do to troubleshoot this?

The user credits log (i'm assuming is the Person Credits option under the admin screen) does not show the credits being added back. In fact, it doesn't even show the transaction to decrease the credits at all.

I checked the error log and there are zero errors there.

Any ideas about how I can dig into this to see what might be occurring?

For example, I just saw someone enter quite a few bookings and all of them except 1 handled the user credits correctly.
They are using Google Chrome 65.0.3325.162 so I asked them to update to a newer version of Chrome to see if it could be a browser based issue.

Which code is being called that updates the user_credit tables?

Yes, the booking_screen_gad screen.
yes, Logins are required

OK. I think I may have found something. Back on Dec 17, 2018, I upgraded PHP to version 7.2.13 and that's about the same time I started seeing the problem.
In the PHP error log, I see:
[24-Jan-2019 11:34:53 America/Chicago] PHP Warning: count(): Parameter must be an array or an object that implements Countable in /data1/webserver/htdocs/components/com_rsappt_pro3/functions2.php on line 667

I'm not sure if this is an ignorable PHP error or not or if upgrading PHP might be the culprit.

Hi Rob,
Please find below:
1. Each user has their own login --> Yes. No one can share logins, we use LDAP for users.
2. Are bookings done via the desktop --> Yes, we are only using the desktop, no mobile phones or jQuery web apps.
3. Do they have access to the Front Desk and thereby the staff booking screen? --> No, only the GAD
4. Is it common to one or two users? --> No, it can happen to anyone.
5. The booking detail shows $0.00 when it fails.
6. Auto Accept is set to Yes (we have been running this for 4 years and it's worked until December 2018).
7. Non-Pay Booking Button is set to No and has been for the last 4 years.

It will show $8 when you are trying to book it on the GAD screen.
When it works, the booking details shows $8.00 and it deducts from the User Credits
When it fails, the booking details shows $0.00 and it doesn't enter a transaction in the User Credits.
I have PayPal set to Yes, but it never calls PayPal because we "give" people credits. When they run out of credits, they can't make any more requests.

Effectively, 1 credit = 1 hour of vacation time. A full day "resource" costs 8 credits (or $8.00). A half day "resource" costs 4 credits (or $4.00). At the beginning of the year, I calculate how many days of vacation time each person receives and then I go to User Credits and increase their Credit Balance to however many days of vacation they get. When someone books a resource, for example 1 day of vacation time, it subtracts 8 credits from their credit "account". Once they get to 0 credits, they are sent to PayPal to buy more, but this isn't real - it sends them to the Test PayPal server and they can't actually "purchase" more vacation time.

1. Joomla Cache:
System Cache: OFF - Caching disabled

2. Resource Rage:
Rate: 1.00 Rate Unit: per Hour

Well, I don't know what was causing the problem, but as quickly as the problem started occurring, it's also disappeared. I do have some SQL that I wrote that I run every day to tell me if the problem returns so I guess I'll just hang loose and see if it happens again.
Thanks for your help.

Well, the problem returned. Can you give me some SQL that will insert/update the appropriate table(s) around user credits so I can just do updates when the problem happens instead of having people cancel and rebook?

Alternately, point me to the file that has the code in it about the user credits and I'll review that and ask questions if I have any.

1. Enable Early Booking Discounts is set to No and has always been. (Just verified it).
2. We use the GAD Booking Screen.
3. Can you tell me what sql I need to use to insert the missing rows in the user_credits and user_credit_activity tables for the bookings that are already missing user credits?