When we create multiple tasks under a single 'Product', the 'Product' selection is not carried over after the first task in the open work item list; therefore, the task fails to link to the Product.

There are no issues when creating the first task; however, for subsequent tasks, the selected 'Product' is not passed from the open work item list, so they don't link correctly.
You can check the update field.
{
"fields": {
"project": {
"id": "10004"
},
"issuetype": {
"id": "10006"
},
"summary": "Araç Tahmini Teslim Tarihi ve Saati girilmesi zorunludur.",
"labels": [],
"customfield_10035": {
"id": "10025",
"value": "C#"
},
"customfield_10032": {
"id": "10259",
"value": "Yeni Filo Online"
},
"customfield_10041": {
"id": "10040",
"value": "Leasing & Rental & Insurance",
"child": {
"id": "10041",
"value": "Scrum 1"
}
},
"customfield_10038": {
"id": "10064",
"value": "Optimum"
},
"customfield_10040": {
"id": "10033",
"value": "Optimum"
},
"customfield_10036": {
"id": "712020:2aa67dac-0fe4-4a8d-9c06-ddae4776e505"
},
"customfield_10039": {
"id": "712020:2aa67dac-0fe4-4a8d-9c06-ddae4776e505"
},
"description": {
"version": 1,
"type": "doc",
"content": [
{
"type": "paragraph",
"content": [
{
"type": "text",
"text": "Araç Tahmini Teslim Tarihi ve Saati girilmesi zorunludur. Bu alan Araç Geliş Tarih ve saatinden daha öncesi olamaz."
}
]
}
]
}
},
"update": {
"issuelinks": [
{
"add": {
"values": [
{
"type": {
"id": "10000"
},
"outwardIssues": [
{
"key": "PRO-1339"
}
]
}
]
}
}
]
},
"watchers": [
"612493fed7cac6006957a226"
],
"externalToken": "0.30898138461634517"
}
However, you will notice that the update field is not populated when opening the second task.
{
"fields": {
"project": {
"id": "10004"
},
"issuetype": {
"id": "10006"
},
"summary": "Araç Tahmini Teslim Tarihi ve Saati girilmesi zorunludur.",
"labels": [],
"customfield_10035": {
"id": "10025",
"value": "C#"
},
"customfield_10032": {
"id": "10259",
"value": "Yeni Filo Online"
},
"customfield_10041": {
"id": "10040",
"value": "Leasing & Rental & Insurance",
"child": {
"id": "10041",
"value": "Scrum 1"
}
},
"customfield_10038": {
"id": "10064",
"value": "Optimum"
},
"customfield_10040": {
"id": "10033",
"value": "Optimum"
},
"customfield_10036": {
"id": "712020:2aa67dac-0fe4-4a8d-9c06-ddae4776e505"
},
"customfield_10039": {
"id": "712020:2aa67dac-0fe4-4a8d-9c06-ddae4776e505"
},
"description": {
"type": "doc",
"version": 1,
"content": [
{
"type": "paragraph",
"content": []
}
]
}
},
"update": {},
"watchers": [
"612493fed7cac6006957a226"
],
"externalToken": "0.24667884991504252"
}
In summary, if the 'Create another' checkbox is checked, the open work items are not being sent for the second task.
Regards