HTTPS monitor says 'unable to get local issuer certificate'

### ⚠️ Please verify that your question has not already been reported - [x] I have searched the [existing issues](https://github.com/louislam/uptime-kuma/issues?q=is%3Aissue%20sort%3Acreated-desc%20) and found no similar reports. ### 🛡️ Security Policy - [x] I have read and agree to Uptime Kuma's [Security Policy](https://github.com/louislam/uptime-kuma/security/policy). ### 📝 Describe your problem One of our numerous HTTPS monitors has been offline since this morning, reporting the error "unable to get local issuer certificate." However, the website itself loads normally when accessed via various web browsers (Firefox and Chrome). The only correlation I can establish is that the monitored system's Let's Encrypt certificate was renewed last night. In case it is relevant: The monitored system is a 3CX phone system that utilizes a built-in automated mechanism for renewing its Let's Encrypt certificates. Several other 3CX systems are being monitored via Uptime Kuma without any issues. If I enable the option to ignore TLS/SSL errors the monitor comes back online - though that defeats the purpose. ### 📝 Error Message(s) or Log ```bash session ``` ### 🐻 Uptime-Kuma Version 2.3.2 ### 💻 Operating System and Arch Debian 13 ### 🌐 Browser Firefox ### 🖥️ Deployment Environment - **Runtime Environment**: - MariaDB: Version `11.8.6` (LTS: Yes/No) - Node.js: Version `24.11.0` (LTS: Yes/No) - **Database**: - MariaDB: Embedded - **Database Storage**: - **Filesystem**: - Linux: ext4 - **Storage Medium**: NVMe - **Uptime Kuma Setup**: - Number of monitors: `350`