Hello! :)

Working of checkpoints can be verified by files in slot directory.
Displaying of progress may differ from reality, especially in first minutes of tasks restart.

OK here is MORE PROOF that checkpoints are NOT working.

It seems not to work for you.
On my win64-systems checkpointing is working ok. I can suspend (LAIM off), restart BOINC, reboot.
Tasks resume from the latest checkpoint with only a few minutes loss at its most.

Application CurieMarieDock on BOINC + zipped input, checkpoints and progress bar 1.00 
Name corona_Eprot_v1_run_2_nb3di_018135_4
State Running
Received 07/06/2021 07:01:32
Report deadline 13/06/2021 07:01:33
Estimated computation size 50,000 GFLOPs
CPU time 06:33:34
CPU time since checkpoint 00:01:37
Elapsed time 06:45:57
Estimated time remaining 01:32:52
Fraction done 77.154%
Virtual memory size 149.04 MB
Working set size 151.33 MB
Directory slots/2
Process ID 1952
Progress rate 11.520% per hour
Executable cmdock-boinc-zcp_wrapper_1.0_windows_x86_64.exe

12-04-2021  13:50               740 target.prm
12-04-2021  13:50           307,542 target.mol2
12-04-2021  13:50         3,260,572 target.as
29-04-2021  02:55         1,543,794 ligands.sdf
06-06-2021  08:19               651 job.xml
06-06-2021  08:19               162 htvs.ptc
07-06-2021  07:01               108 cmdock-boinc-zcp_wrapper_1.0_windows_x86_64.exe
07-06-2021  07:01                 0 boinc_lockfile
07-06-2021  07:01               212 stderr.txt
07-06-2021  07:01                 8 docking_out.sd
07-06-2021  09:32             8,641 init_data.xml
07-06-2021  13:01                12 docking_out.progress
07-06-2021  13:08                22 docking_out.chk
07-06-2021  13:40            49,251 docking_log
07-06-2021  13:47            97,386 docking_out.log
07-06-2021  13:47                29 wrapper_checkpoint.txt
07-06-2021  13:47               512 boinc_task_state.xml