Boot much slower after partition resize

Problem solved! Because I moved the swap partition, it had changed UUID. The mismatch in fstab caused the delay, it seems. Found the answer here: Very slow boot with Ubuntu 15.04

One possible cause may be incorrect partition alignment.

Proper partition alignment is essential for optimal performance and longevity. This is due to the block nature of every I/O operation on the hardware level as well as file system level. The key to alignment is partitioning to (at least) the given block size, which depends on the used hardware. If the partitions are not aligned to begin at multiples of the block size, aligning the file system is a pointless exercise because everything is skewed by the start offset of the partition.

Solid state drives are based on flash memory, and thus differ significantly from hard drives. While reading remains possible in a random access fashion, erasure (hence rewriting and random writing) is possible only by whole blocks. Additionally, the erase block size (EBS) are significantly greater than regular block size, for example 128KiB vs. 4KiB, so it is necessary to align to multiples of EBS.

(from ArchLinux wiki)

To verify a partition is aligned, query it using /usr/bin/blockdev as shown below, if a '0' is returned, the partition is aligned:

sudo blockdev --getalignoff /dev/<partition>