Interesting! Small leaves are usually caused by either pests or a lack of light. Check for thrips – you never know! Copper-coloured patches on the white parts of the leaves can be a sign. I like to use predatory mites, but a lot of people prefer a systemic pesticide.

Small leaves could also indicate a light issue – it probably got used to having a tonne of energy from having so many leaves so now it’s been cut back it’s struggling to produce mature leaves. Try moving it closer to the window to spur it on to grow bigger leaves – once it gets back into the swing of things you can move it back and it may continue growing big leaves just fine.

The problem with old vining plants is that the leaves naturally drop as they age, so the original plant can end up looking a little sparse. I’m confident that you can keep doing whatever you’re doing with regards to watering/feeding/repotting because it won’t suddenly have decided that you were doing it wrong for the past 30 years.