Cannot strict parse date with timezone (ZZ)

[ledenis]

Describe the bug

Parsing a date in strict mode (with customParseFormat plugin) with timezone (ZZ / +0600) returns a date object which is not .isValid().

const dayjs = require("dayjs");
const customParseFormat = require("dayjs/plugin/customParseFormat");

dayjs.extend(customParseFormat);

const dateFormat = "YYYYMMDD HHmmss ZZ";

const date = dayjs("20241224 061500 +0600", dateFormat);
console.log("date.isValid()", date.isValid()); // true
console.log("isoString", date.toISOString()); // 2024-12-24T00:15:00.000Z

const dateStrict = dayjs("20241224 061500 +0600", dateFormat, true);
console.log("dateStrict.isValid()", dateStrict.isValid()); // false <---------- WRONG
console.log("isoString", dateStrict.toISOString()); // throws RangeError: Invalid time value

Expected behavior

• dateStrict.isValid() should return true
• dateStrict.toISOString() should not throw RangeError: Invalid time value, it should return 2024-12-24T00:15:00.000Z

Information

• Day.js Version: v1.11.13
• OS: Linux Mint 20.2
• Node v20.10.0
• Time zone: Europe/Paris