Based on the yeast being weeks old from purchase, I'd agree that the issue was caused by underproofing due to age of yeast reducing viability.
Ideally you'd get a new packet of yeast, though the same old yeast can still be used by 1) adding additional yeast to account for reduced viability, or 2) gently nursing the yeast to recover while rehydrating - both will require some experimentation.
For option 2), assuming you are mixing the dry yeast directly into the dough and not rehydrating and tempering the yeast beforehand, there is an article published on rehydrating lager yeast for increased viability referenced below - in short:
- sprinkle mass of yeast onto 10x yeast mass of water at 25C-30C
- allow yeast to slowly hydrate undisturbed for 15 minutes
- gently stir yeast and water to form a slurry
- allow yeast to acclimate undisturbed for at least another 15 minutes
Figure of one rehydrated yeast from "Rehydration of Active Dry Brewing Yeast and its Effect on Cell Viability". A=immediately after sprinkling on water, B=15 minutes after sprinkling, Cn=15 minute intervals after forming slurry.
An additional step you can add is 'proofing' or 'proving' the yeast with some added sugar - generally, a step used to verify yeast activity with gas formation, though it will also provide some nourishment to restart yeast metabolism before incorporating into dough. The King Arthur Baking Company and a MasterClass article describe the procedures; you can also replace a quarter of the added sugar with flour to provide the yeast with protein for reproduction and to acclimate it to amylose metabolism. I'd recommend forming the slurry before adding sugar and flour to avoid further osmotic stress during rehydration.
Rehydration of Active Dry Brewing Yeast and its Effect on Cell Viability.
D. M. Jenkins, C. D. Powell, T. Fischborn and K. A. Smart.
Additionally, the small cracking throughout the top surface of the loaf and the 'pinched' appearance of the left two score marks suggest the scoring might not be deep enough - the cracks specifically are a sign that gas expansion is being restricted by the hardened crust until pressure builds up enough to tear the crust.
You may have better oven spring by scoring a little deeper as well.