delay when unlocking

When I "lock" the session, and then I "unlock", I see a black screen for about 5 seconds before the desktop shows. I have a relatively high-spec system so this seems to be unusual behavior.
But after a reboot, I get from from the lock screen to desktop quite fast.

My Manjaro installation was originally the default Xfce version. I added KDE desktop and activated the recommended desktop manager.

System info:

inxi -F
  Host: shmuel-manjaroxfce Kernel: 5.4.40-1-MANJARO x86_64 bits: 64 
  Desktop: KDE Plasma 5.18.5 Distro: Manjaro Linux 
  Type: Desktop Mobo: ASUSTeK model: PRIME B365M-A v: Rev X.0x 
  serial: <root required> UEFI: American Megatrends v: 1203 date: 10/10/2019 
  Topology: 8-Core model: Intel Core i7-9700 bits: 64 type: MCP L2 cache: 12.0 MiB 
  Speed: 834 MHz min/max: 800/4700 MHz Core speeds (MHz): 1: 800 2: 800 3: 800 
  4: 800 5: 800 6: 800 7: 800 8: 800 
  Device-1: Intel UHD Graphics 630 driver: i915 v: kernel 
  Display: x11 server: X.Org 1.20.8 driver: intel unloaded: modesetting 
  resolution: 1920x1080~60Hz 
  OpenGL: renderer: Mesa Intel UHD Graphics 630 (CFL GT2) v: 4.6 Mesa 20.0.6 
  Device-1: Intel 200 Series PCH HD Audio driver: snd_hda_intel 
  Device-2: JMTek LLC. type: USB driver: hid-generic,snd-usb-audio,usbhid 
  Sound Server: ALSA v: k5.4.40-1-MANJARO 
  Device-1: Realtek RTL8111/8168/8411 PCI Express Gigabit Ethernet driver: r8169 
  IF: enp3s0 state: up speed: 1000 Mbps duplex: full mac: a8:5e:45:e2:87:3c 
  Local Storage: total: 2.26 TiB used: 1.05 TiB (46.6%) 
  ID-1: /dev/sda vendor: Kingston model: SA400S37480G size: 447.13 GiB 
  ID-2: /dev/sdb vendor: Toshiba model: HDWD120 size: 1.82 TiB 
  ID-1: / size: 102.49 GiB used: 14.08 GiB (13.7%) fs: ext4 dev: /dev/sda6 
  System Temperatures: cpu: 29.8 C mobo: 27.8 C 
  Fan Speeds (RPM): N/A 
  Processes: 247 Uptime: 49m Memory: 15.50 GiB used: 10.59 GiB (68.3%) Shell: bash 
  inxi: 3.0.37 

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