I think the longest I've gone without a sale was 10 months only to have 3 xxxx sales by the 11th month.
As long as you have good names, the sale will come. It's always a matter of time. However, that time may span over several years for some certain types of names.
Not everyone is cut out for the long wait. If you fall into that category of sellers, your best bet is to go for flipping liquid names with small margins like 3L, 4L, 3N, 4N and 5N .coms and maybe some Geo names.
Oh, portfolio size always hovers between 150 - 200 names for me. I also have a good job, so that keeps me motivated during dry spells in domaining. Domaining is my side gig