Postgres upgrade(10.9 to 12.2) is failing sporadically

Question

Postgres upgrade(10.9 to 12.2) is failing sporadically

1. We have upgraded postgres cluster from 10.5 to 12.2
2. 10.5 version has also has extension lib PLV8. But we want to get rid of that extension in the upgraded version (12.2)
3. Before upgrade, we have removed the extension (PLV8) and dropped all the related stored procedures.
4. Created new cluster with 12.2 version and then used pg_upgrade command from that binary location.
5. First we used 'check' and if succeeds then used 'link' for upgrade.

But we observed, upgrade fails sometimes at 'check' step (pg_upgrade --check) and some other times fails at 'link' (pg_upgrade --link) step though check step was success.

with below logs

pg_upgrade --check fails with below output

[-----------------------------]
[Performing Consistency Checks]
[Checking cluster versions                                   ok]
[Checking database user is the install user                  ok]
[Checking database connection settings                       ok]
[Checking for prepared transactions                          ok]
[Checking for reg* data types in user tables                 ok]
[Checking for contrib/isn with bigint-passing mismatch       ok]
[Checking for tables WITH OIDS                               ok]
[Checking for invalid "sql_identifier" user columns          ok]
[]
[*failure*]
[]

Failed at "Checking for presence of required libraries"

some other times pg_upgrade --link fails with below output

[-----------------------------]
[][Checking cluster versions                                   ok]
[Checking database user is the install user                  ok]
[][Checking database connection settings                       ok]
[][Checking for prepared transactions                          ok]
[][Checking for reg* data types in user tables                 ok]
[][Checking for contrib/isn with bigint-passing mismatch       ok]
[][Checking for tables WITH OIDS                               ok]
[][Checking for invalid "sql_identifier" user columns          ok]
[][Creating dump of global objects                             ok]
[][Creating dump of database schemas]
[][  postgres]

[][*failure*]

Failed at "Checking for presence of required libraries"

Note:

1. Failure is sporadic
2. Both link and check are failing at phase of "Checking of required libraries"
3. Problem is getting only on VMs.