Non-uniform adding times while uploading to Backblaze B2

I’m backing up my photos (~30GB) to Backblaze B2 and am noticing weird “saved in” duration. An excerpt:

new       /Camera/20191211_114821.jpg, saved in 1.303s (4.694 MiB added)
new       /Camera/20191211_114820.jpg, saved in 36.277s (4.942 MiB added)
new       /Camera/20191211_114835.jpg, saved in 9.371s (4.000 MiB added)
new       /Camera/20191211_114837.jpg, saved in 21.874s (4.873 MiB added)
new       /Camera/20191211_114838.jpg, saved in 25.710s (5.146 MiB added)
new       /Camera/20191211_114844.jpg, saved in 12.054s (4.952 MiB added)
new       /Camera/20191211_114834.jpg, saved in 1078.527s (4.077 MiB added)
new       /Camera/20191211_114909.jpg, saved in 1044.494s (6.731 MiB added)
new       /Camera/20191211_114912.jpg, saved in 1048.691s (5.554 MiB added)
new       /Camera/20191211_114936.mp4, saved in 12.423s (3.037 MiB added)
new       /Camera/20191211_114944.jpg, saved in 16.760s (2.984 MiB added)
new       /Camera/20191211_114950.jpg, saved in 16.803s (2.934 MiB added)
new       /Camera/20191211_114926.jpg, saved in 35.016s (2.906 MiB added)
new       /Camera/20191211_115104.jpg, saved in 5.747s (1.694 MiB added)
new       /Camera/20191211_115108.jpg, saved in 0.110s (1.745 MiB added)
new       /Camera/20191211_115055.jpg, saved in 17.501s (1.685 MiB added)
new       /Camera/20191211_115115.jpg, saved in 19.529s (5.179 MiB added)
new       /Camera/20191211_120230.jpg, saved in 13.070s (4.675 MiB added)
new       /Camera/20191211_120232.jpg, saved in 5.277s (4.457 MiB added)
new       /Camera/20191211_115148.jpg, saved in 25.235s (1.688 MiB added)
new       /Camera/20191211_120318.jpg, saved in 21.630s (3.622 MiB added)
new       /Camera/20191211_120311.jpg, saved in 23.891s (4.188 MiB added)
new       /Camera/20191211_120434.jpg, saved in 2.224s (3.957 MiB added)
new       /Camera/20191211_120323.jpg, saved in 41.161s (6.243 MiB added)
new       /Camera/20191211_120547.jpg, saved in 17.851s (2.817 MiB added)
new       /Camera/20191211_120551.jpg, saved in 0.155s (2.703 MiB added)
new       /Camera/20191211_120454.jpg, saved in 19.992s (5.914 MiB added)
new       /Camera/20191211_120603.jpg, saved in 5.737s (3.052 MiB added)
new       /Camera/20191211_120907.jpg, saved in 3.875s (6.031 MiB added)
new       /Camera/20191211_120904.jpg, saved in 13.029s (5.779 MiB added)

Any idea how I can improve this? Network has been fairly stable.

How fast are you able to upload files to B2?

Have you played with -o b2.connections=n?