Launchd runs old scripts, but won't run new scripts

I'm sure this is something simple. Be that as it may, I can't figure it out.

I've been writing simple shell scripts for years that I run via launchd plist files created with Lingon. Generally that works fine unless I do something dumb which is not all that rare.

However, after installing Sonoma, I can't get launchd to run new scripts on either an old Intel iMac or a newer M1 MBA.

To keep things simple, I've written a very brief shell script along with a very minimal launchd plist:

Sellotape:bin mnewman$ cat ldtest.sh
#!/bin/bash
# shell script to test launchd
now=$(date +%Y-%m-%d-%H%M)
echo $now " hello" >> /users/mnewman/public/ldtest.log
exit 0

Sellotape:LaunchAgents mnewman$ cat com.mgnewman.ldtest.plist
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>EnvironmentVariables</key>
<dict>
<key>PATH</key>
<string>/usr/local/bin:/System/Cryptexes/App/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/Library/Apple/usr/bin:/Library/Frameworks/Mono.framework/Versions/Current/Commands:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/local/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/appleinternal/bin:/usr/local/sbin:/opt/local/bin</string>
</dict>
<key>Label</key>
<string>com.mgnewman.ldtest</string>
<key>ProgramArguments</key>
<array>
<string>/Users/mnewman/bin/ldtest.sh</string>
</array>
<key>RunAtLoad</key>
<true/>
<key>StandardErrorPath</key>
<string>/Users/mnewman/public/error.log</string>
<key>StandardOutPath</key>
<string>/Users/mnewman/public/output.log</string>
<key>StartCalendarInterval</key>
<array>
<dict>
<key>Hour</key>
<integer>11</integer>
<key>Minute</key>
<integer>40</integer>
</dict>
</array>
</dict>
</plist>

If I run the script from the command line it works as expected. However, launchd will not run it. I've sat there and watched the console scroll by at the time it should be running and there's nothing.

Lingon's test facility reports no errors and there's nothing in Lingon's log file.

Sellotape:public mnewman$ launchctl list | grep mgnewman
-    0    com.mgnewman.ldtest
-    0    com.mgnewman.deljpeg
-    0    com.mgnewman.volume
-    0    com.mgnewman.ip
-    0    com.mgnewman.chaamyt

It's the first one. The other four are older and run reliably.

And:

Sellotape:public mnewman$ launchctl print-disabled gui/501/com.mgnewman.* | grep mgnewman
        "com.mgnewman.deljpeg" => enabled
        "com.mgnewman.ldtest" => enabled
        "com.mgnewman.mailtest" => disabled
        "com.mgnewman.volume" => enabled
        "com.mgnewman.chaamyt" => enabled

It's the second one, so enabled for launchd.

So, what silly thing have I done this time? I'm sure it's something simple, but beyond my feeble brain to uncover.