Yes, That's a key statement - ZWave, by default, is "unsupervised" communication - Basically, fire and forget, and hope the other end gets the request or update.. So my other recommendation, is to potentially enable S2 security on these 19 nodes, to get more error correction/CRCs that comes along with the encryption. It's not clear to me, if all your 19 devices support S2, and your still effectively flooding the Zwave mesh with a bunch of requests, and the expected state replies. So the weakest link is still likely to fail.
See: End Nodes: Guidelines for communication with S2+Supervision · Issue #5471 · zwave-js/node-zwave-js · GitHub & [GUIDE] Writing Z-Wave Drivers for S2
The other options, noted above, it either use the "All Off" app, or if you just want to do this in RM, send the command for all off (to with the switch enabled for just those devices that are on) - Then wait 2 secs, refesh all these nodes, to force a current state update, and then issue the same command above. Bottom line, and as you've learned, unsupervised Zwave (the default) isn't the most "reliable" network protocol, think UDP
Or better yet, move off ZWave to Matter, which is a more recent protocol that requires updates and handshaking to support the multi-admin function feedback. I'm guessing that's not an option for 19 devices, but YMMV
