What are the byproducts in a Suzuki reaction?
It is postulated that the trifluroborates are not the transmetallating specis, rather than to be the source of slow hydrolysis to yield boronic acids:

(source 1, slide 41; citing Molander and Biolatto, 2003 (Ref.1))
which then enter the catalytic cycle:

(preview in Kürti &amp; Czakó, page 448 bottom (Ref.2)
Organic Reactions (vide infra) explicitly states that complete hydrolysis of the trifluoroborates is necessary to allow successful transmetallation.
In addition, the fluoride anion is said to interact in the following way with the palladium catalyst:

(source 2)

References:

Gary A. Molander, Betina Biolatto, &quot;Palladium-Catalyzed Suzuki−Miyaura Cross-Coupling Reactions of Potassium Aryl- and Heteroaryltrifluoroborates,&quot; J. Org. Chem. 2003, 68(11), 4302-4314 (https://doi.org/10.1021/jo0342368).
László Kürti, Barbara Czakó, In Strategic Applications of Named Reactions in Organic Synthesis: Background and Detailed Mechanisms; Forwarded by E. J. Corey, Introduction by K. C. Nicolaou; Elsevier Academic Press: Burlington, MA, 2005 (ISBN-13: 978-0-12-429785-2).