Gas oven clicks but won't ignite — what should I check?

That delayed "whump" is worth fixing promptly — gas is pooling before it lights. Likely causes:

1. Weak or failing igniter. Most gas ovens use a glow-bar or spark igniter. If it's weak, gas flows before the igniter is hot/strong enough to light it — hence the delay and the "whump". Most common cause, and a straightforward part replacement.
2. Blocked/dirty burner ports. Grease and food clog the oven burner so it lights unevenly. Cleaning the ports can restore a quick, clean light.
3. Gas supply/pressure to the oven burner specifically.

Safety: if you smell gas strongly, stop and turn off the supply — the delayed ignition means unburnt gas is building up. Since the hob works, your main supply is fine; this is specific to the oven burner. Get the igniter checked rather than living with it.