This just happened to me as well. Done about 10 transfers from Chase to United, usually a segment at a time so about 60k max, and had never waited more than a couple of minutes and lost availability.

On 4/23 I initiated a 150k point transfer to book 2 round trips for my honeymoon. When it hadn't shown up in a couple of hours I feared losing availability and called Cardmember Services. They told me there's really nothing they could do until 7 days had passed. I wasn't about to initiate another transfer and get stuck with twice the United points I needed, so I was going to wait the 7 days and cross my fingers my honeymoon wasn't doomed.

On 4/28 (5 days later), the points finally showed up in my United account. Despite ticket availability going to 0 in the last few days and completely freaking out, theres actually more availability now. Got very lucky.

This is absolutely unacceptable given the state of booking award tickets.