Ubuntu 18 doesn't wake up once the display goes blank

I have installed Ubuntu 18 recently on my AMD Ryzen 5 2400G CPU. We know that Ubuntu automatically locks and turn off the display after a specific time of inactivity. Once my display goes black like this, I am unable to get it back to the normal state. That is, the monitor remains black irrespective of whatever I do. I tried pressing keys, tapping mouse and even disconnected and reconnected the monitor cable. Nothing happens.

I could listen my CPU is working fine from the sound of fan, that is it didn't go to sleep. Each time this happens, I have to do a hard restart to get things working again. This is really annoying. Is this a known bug? I searched the community but couldn't find anything worth noticing.

For instance, my machine details:

anony@Anony:~$ uname -a
Linux Anony 4.15.0-33-generic #36-Ubuntu SMP Wed Aug 15 16:00:05 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
anony@Anony:~$ lsb_release -r
Release:    18.04
anony@Anony:~$ lscpu
Architecture:        x86_64
CPU op-mode(s):      32-bit, 64-bit
Byte Order:          Little Endian
CPU(s):              8
On-line CPU(s) list: 0-7
Thread(s) per core:  2
Core(s) per socket:  4
Socket(s):           1
NUMA node(s):        1
Vendor ID:           AuthenticAMD
CPU family:          23
Model:               17
Model name:          AMD Ryzen 5 2400G with Radeon Vega Graphics
Stepping:            0
CPU MHz:             1578.024
CPU max MHz:         3600.0000
CPU min MHz:         1600.0000
BogoMIPS:            7186.54
Virtualization:      AMD-V
L1d cache:           32K
L1i cache:           64K
L2 cache:            512K
L3 cache:            4096K
NUMA node0 CPU(s):   0-7
Flags:               fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm constant_tsc rep_good nopl nonstop_tsc cpuid extd_apicid aperfmperf pni pclmulqdq monitor ssse3 fma cx16 sse4_1 sse4_2 movbe popcnt aes xsave avx f16c rdrand lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw skinit wdt tce topoext perfctr_core perfctr_nb bpext perfctr_llc mwaitx hw_pstate sme ssbd ibpb vmmcall fsgsbase bmi1 avx2 smep bmi2 rdseed adx smap clflushopt sha_ni xsaveopt xsavec xgetbv1 xsaves clzero irperf xsaveerptr arat npt lbrv svm_lock nrip_save tsc_scale vmcb_clean flushbyasid decodeassists pausefilter pfthreshold avic v_vmsave_vmload vgif overflow_recov succor smca