Do modern ovens bake the same as the old ones? Is the new oven the reason popovers don't rise?
I'd guess it's not the new oven that's wrong, but the old one.
Older ovens has less accurate thermometers &amp; were maybe 20° hotter at the top than the bottom. The chances are your hand-me-down recipe was based on this phenomenon &amp; your new one is accurate… &amp; therefore not hot enough.
I'd never heard of popovers until 10 minutes ago, but reading through recipes online, they seem to be exactly same as Yorkshire Puddings, just served with sweet toppings instead of roast beef &amp; gravy. [How two sides of the Atlantic arrived at that difference, I'll never know nor understand ;)
Most say to use 450°F [230°C] which is more like I'd use for Yorkies - in fact for Yorkies, the hotter the better, preheat your tins too. My rule of thumb has always been, once everything else is done [roast dinner, remember;) just turn the heat to max, add your oil &amp; put your tins in the top half [high as you can but leaving room to rise], then give it 15 mins to come up to temperature. The oil should be smoking before you drop your batter.
Pour quickly &amp; get that door shut. Once in, never open the door until they're ready.
After comments
I've never known anyone to drop the temperature half-way through [but then again, 'crispy' is not something I'd want from a yorkie [only supermarkets &amp; restaurants think they should be crispy, ordinary Yorkshire folks don't]), but I still think you're not getting enough heat into them right at the start.
Maybe your oven really does slump the temperature easily; maybe you've got the door open too long or the element isn't fast enough to get back up to temperature; tins aren't hot enough to start with.
I'd try at least once with the oven simply &quot;on full&quot; - whatever it thinks it can go to - but watch it doesn't switch mode right at the top. if I turn mine full then back it switches to rotisserie/fan grill rather than 'oven'. That might be a little excessive ;)