Lost lock ~2:30 hours ago, took 1:30 hours to get it back. I had initially switched BSC blends to 90 mhz blends because useism was down and winds were higher. I also suspected the 45mhz blends were causing the low frequency motion seem in some of the CR FOMs. After not making much progress, I tried switching back (to the 45mhz blends), but ALS-x then refused to stay locked. We are now back to observing, with 90mhz blends. The occasional bursts of low frequncy motion we were getting on IMC-F & (I think) ALS-Y Refl (or one of the Drive Aligns), and the ASC traces have not returned. Useism has been below .4 microns my entire shift, winds variable but below 20 mph.