Troubleshooting Lookup Issues Between Tables A and B in CRM

Hello I have 2 tables, lets say table A and B. Table A has company domains of each new inbound lead. I used lookup multiple rows to pull the company domains into Table B. Table A enriches the lead that has come in Table B enriches the company (doing it in separate tables to make sure that we can send the info about the company to the right deal page). So every time a lead comes in to our crm, it goes into clay table A and enriches him/her. Now to enrich the company, we're using the domain from table A using multiple rows lookup. Problem - when a new lead comes in, the Table A gets updated, but Table B doesn't (the lookup) Can you help please?