Why do transfers from bank take SO long?

I initiated a transfer from my CapitalOne account on March 2.
CapitalOne showed it complete on March 6.
It’s now March 9 and my Stessa account still shows it pending.

Same here but my Stessa account not showing it pending and I’m new to Stessa. So, now I’m worried tenant’s $2300 is loss. My tenant is getting furious because they can’t move in until I receive funds and his bank shows the funds were taken out of his account. Is there customer support we can call ?