This error happens all the time - I thought it was a temporary bug, but no - it appears on all the projects I did, old and new. Here's how it goes: 1. Create a new project, new schematic 2. Add a few capacitors, for example in my recent case it was LCSC component C118884, connect them into a circuit, save the schematic 3. Make a PCB from it, place the components, save it 4. Change something in the schema, e.g. add a resistor, connect it to the circuit, save it 5. In the PCB, click "import changes" from the schema, everything goes ok 6. Now, close everything and log out 7. Open the same schema again, open the PCB 8. In the PCB, click "Import changes" from the schema 9. The bug happens - suddenly it cannot find the packages from 5 minutes ago. This happens all the time.