Yes, the message "wlan0: DHCP lease expired" indicates that the IP address lease for your Raspberry Pi's wireless interface (wlan0) has ended. This could very well be the reason you're unable to connect to your Raspberry Pi via SSH, especially if the Pi doesn't successfully renew its IP address lease. If the Raspberry Pi doesn't obtain a new IP address or reverts to a different address after the lease expires, any connection using the old IP will fail.

Here's what you can do to diagnose and potentially solve the issue:

1. **Static IP Configuration**: 
   - Consider assigning a static IP address to your Raspberry Pi. This will ensure that the IP address remains constant, preventing disruptions due to DHCP lease expirations. 
   - To set a static IP, you can edit the `/etc/dhcpcd.conf` file and add:
     ```
     interface wlan0
     static ip_address=192.168.x.x/24
     static routers=192.168.x.1
     static domain_name_servers=192.168.x.1
     ```
     Replace the `x` with appropriate numbers for your network setup.

2. **Check DHCP Lease Duration**:
   - If you have access to your router's settings, look for the DHCP lease duration setting. Some routers are set to have short lease durations by default. Increasing the lease duration might help. 

3. **Reconnect Script**: 
   - Write a script that checks for network connectivity and restarts the network interface if the network is down. This can help to reconnect if the DHCP lease expires and isn't renewed.
   - Here's a basic example:
     ```bash
     #!/bin/bash
     if ! ping -c 1 8.8.8.8; then
         sudo ifconfig wlan0 down
         sleep 5
         sudo ifconfig wlan0 up
     fi
     ```
   - You can run this script regularly using a cron job.

4. **Logs and Diagnostics**:
   - Check the system logs for any other related messages or errors. Use `dmesg` or `journalctl` to view the logs.
   - Specifically, you can filter the logs related to the wireless interface using:
     ```
     journalctl | grep wlan0
     ```

5. **Update & Upgrade**:
   - Sometimes, simply updating the Raspberry Pi can solve network-related issues. Ensure your Raspberry Pi's OS and firmware are updated:
     ```
     sudo apt update
     sudo apt upgrade
     sudo rpi-update
     ```

6. **Wi-Fi Signal & Interference**:
   - Ensure your Raspberry Pi is within a good range of your Wi-Fi router. Weak signals can cause intermittent connectivity issues.
   - Also, other electronic devices or neighboring Wi-Fi networks can interfere with the Wi-Fi signal. Try changing the Wi-Fi channel on your router if you suspect interference.

Remember, while assigning a static IP can help with the SSH issue, it's important to ensure that the static IP you assign doesn't conflict with any other device on your network. Always choose an IP outside of the DHCP range set on your router, or reserve the IP specifically for your Raspberry Pi in the router's settings.
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