In client script (on inventory detail) when i return false on validateField i get infinities loop of the alert... (chrome issue) anyone know how to solve this issue?

function validateField(scriptContext) {
            let rec = scriptContext.currentRecord;
            let sublist = scriptContext.sublistId;
let field= scriptContext.fieldId;
            let flag = true;

            if (sublist === 'inventoryassignment' && field === 'receiptinventorynumber') {
                let invNum = rec.getCurrentSublistText(sublist, 'receiptinventorynumber');

                if (isLotExists(invNum)) {
                        alert(`Lot Number: ${invNum} is already exists in inventory`)
                        flag = false;
                    } else {
                    flag = true;
                }
            }
            return flag;
        }