Hi,
We are talking about HF. Thus this still is far away from being a GND plane.
All the traces have the same length as before ... and for HF the width doesn´t play much a role.
Simple method: Use double layer. Make the whole layer GND without any other traces/signals.
Use short traces to connect each single GND line with a via to GND plane.
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Are you sure your "secret U1" has no GND connection?
I assume the U1 connection is wrong/inclomplete. I see only one resistive connection to the other circuit, any other signals are either floating or have a capacitor in series.
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But as long as you hide most informations like part names, values, schematic, description ... it´s useless to go on guessing.
Klaus