A value is missing sometimes from "before display" to "before record added"

Hi. This case is weird. I am not able to debug and I am asking for ideas from you.

I have a list page with a button where I call to an add page using two parameters. iID and aID obtained in this first page. Code:

$record = $button->getCurrentRecord();
$_SESSION["alumnosID"] = $result["alumnosID"] = $record["alumnosID"];
$result["SUBSYSTEMLOCATION"] = $SUBSYSTEMLOCATION . "/" . "eainvest17_add.php?aID=" . $_SESSION["alumnosID"] . "&" . "iID=" .  $_SESSION["investigadoresID"];

The eainvest17_add.php page works most of the time (around 3-4% of the time I lost this value: $_SESSION["alumnosID"] when traversing from "Before display" and "Before record added"

I modify my code to generate logs and review this. I confirmed this is happening. I am not sure why and this is my request for help.

Here is the code that add to a log file for all the following examples:

error_log("<<message in page>>: |" . date("Y-m-d h:i:s") . "|" . $_SESSION["UserID"] . "|" . $_SESSION["investID"] . "|" . $_SESSION["alumnosID"]  . "|" . $_SERVER[REQUEST_URI] .  "|\n", 3, $logfile);

The following examples shows the expected result (96-97% of the time is like this)

Quote

Before display: |2018-09-05 09:37:08|HIBC750513|8216|180470|/verano18/investigadores/eainvest17_add.php?aID=180470&iID=8216|
Before record added 1: |2018-09-05 09:45:27|HIBC750513|8216|180470|/verano18/investigadores/eainvest17_add.php?submit=1&|
Before record added 2: |2018-09-05 09:45:27|HIBC750513|8216|180470|/verano18/investigadores/eainvest17_add.php?submit=1&|
After record added: |2018-09-05 09:45:27|HIBC750513|8216|180470|/verano18/investigadores/eainvest17_add.php?submit=1&|
Before display: |2018-09-05 09:45:27|HIBC750513|8216|180470|/verano18/investigadores/eainvest17_add.php?submit=1&|||

Before display: |2018-09-05 09:33:17|MAMM681228|10219|180248|/verano18/investigadores/eainvest17_add.php?aID=180248&iID=10219|
Before record added 1: |2018-09-05 09:49:05|MAMM681228|10219|180248|/verano18/investigadores/eainvest17_add.php?submit=1&|
Before record added 2: |2018-09-05 09:49:05|MAMM681228|10219|180248|/verano18/investigadores/eainvest17_add.php?submit=1&|
After record added: |2018-09-05 09:49:06|MAMM681228|10219|180248|/verano18/investigadores/eainvest17_add.php?submit=1&|
Before display: |2018-09-05 09:49:06|MAMM681228|10219|180248|/verano18/investigadores/eainvest17_add.php?submit=1&|

Before display: |2018-09-05 09:49:12|MAMM681228|b|/verano18/investigadores/eainvest17_add.php?aID=181910&iID=10219|
Before record added 1: |2018-09-05 10:00:49|MAMM681228|10219|181910|/verano18/investigadores/eainvest17_add.php?submit=1&|
Before record added 2: |2018-09-05 10:00:49|MAMM681228|10219|181910|/verano18/investigadores/eainvest17_add.php?submit=1&|
After record added: |2018-09-05 10:00:51|MAMM681228|10219|181910|/verano18/investigadores/eainvest17_add.php?submit=1&|
Before display: |2018-09-05 10:00:51|MAMM681228|10219|181910|/verano18/investigadores/eainvest17_add.php?submit=1&|

Before display: |2018-09-05 10:00:55|MAMM681228|10219|182051|/verano18/investigadores/eainvest17_add.php?aID=182051&iID=10219|
Before record added 1: |2018-09-05 10:03:41|MAMM681228|10219|182051|/verano18/investigadores/eainvest17_add.php?submit=1&|
Before record added 2: |2018-09-05 10:03:41|MAMM681228|10219|182051|/verano18/investigadores/eainvest17_add.php?submit=1&|
After record added: |2018-09-05 10:03:41|MAMM681228|10219|182051|/verano18/investigadores/eainvest17_add.php?submit=1&|
Before display: |2018-09-05 10:03:41|MAMM681228|10219|182051|/verano18/investigadores/eainvest17_add.php?submit=1&|

Before display: |2018-09-05 09:49:46|BAIL520916|1638|182289|/verano18/investigadores/eainvest17_add.php?aID=182289&iID=1638|
Before record added 1: |2018-09-05 10:14:47|BAIL520916|1638|182289|/verano18/investigadores/eainvest17_add.php?submit=1&|
Before record added 2: |2018-09-05 10:14:47|BAIL520916|1638|182289|/verano18/investigadores/eainvest17_add.php?submit=1&|
After record added: |2018-09-05 10:14:47|BAIL520916|1638|182289|/verano18/investigadores/eainvest17_add.php?submit=1&|
Before display: |2018-09-05 10:14:47|BAIL520916|1638|182289|/verano18/investigadores/eainvest17_add.php?submit=1&|

You can notice the url has the same values in the log records as stated by the call with aID and iID (as expected)

But sometimes, just sometimes and I have no clue to this The logs shows the following (you can see the aID is missing and because of that the values recorded in the proper record has NULL which is an error. I have to fix those NULL values by hand now.

Quote

Before display: |2018-09-03 07:32:34|PEPR540306|||/verano18/investigadores/eainvest17_add.php?aID=180246&iID=13482|
Before record added 1: |2018-09-03 07:39:32|PEPR540306|13482||/verano18/investigadores/eainvest17_add.php?submit=1&|
Before record added 2: |2018-09-03 07:39:32|PEPR540306|13482||/verano18/investigadores/eainvest17_add.php?submit=1&|
After record added: |2018-09-03 07:39:32|PEPR540306|13482||/verano18/investigadores/eainvest17_add.php?submit=1&|
After record added NULL confirmed: |2018-09-03 07:39:32|PEPR540306|13482||/verano18/investigadores/eainvest17_add.php?submit=1&|
Before display: |2018-09-03 07:39:32|PEPR540306|||/verano18/investigadores/eainvest17_add.php?submit=1&|||

Before display: |2018-09-05 07:50:44|MACB730827|10247|183772|/verano18/investigadores/eainvest17_add.php?aID=183772&iID=10247|
Before record added 1: |2018-09-05 08:45:23|MACB730827|10247||/verano18/investigadores/eainvest17_add.php?submit=1&|
Before record added 2: |2018-09-05 08:45:23|MACB730827|10247||/verano18/investigadores/eainvest17_add.php?submit=1&|
After record added: |2018-09-05 08:45:23|MACB730827|10247||/verano18/investigadores/eainvest17_add.php?submit=1&|
After record added NULL confirmed: |2018-09-05 08:45:23|MACB730827|10247||/verano18/investigadores/eainvest17_add.php?submit=1&|
Before display: |2018-09-05 08:45:24|MACB730827|||/verano18/investigadores/eainvest17_add.php?submit=1&|

I really appreciate any idea. I am lost with this.

Regards to all.