We have one managed package Visualforce UI <apex:commandButton .../> timing out only in Spring ‘20 Sandbox Preview orgs. The tail end of the log looks like this:
11:42:28.5 (1587639757)|VARIABLE_ASSIGNMENT|[EXTERNAL]|this|{}|0x13e6c054
11:42:28.5 (1587652325)|STATEMENT_EXECUTE|[80]
11:42:28.5 (1587655972)|STATEMENT_EXECUTE|[81]
11:42:28.5 (1587658790)|STATEMENT_EXECUTE|[84]
11:42:28.5 (1587717838)|HEAP_ALLOCATE|[1084]|Bytes:5
11:42:28.5 (1587726691)|SYSTEM_MODE_EXIT|false
11:42:28.5 (1587735431)|HEAP_ALLOCATE|[1084]|Bytes:5
11:42:28.5 (1592110360)|VF_SERIALIZE_VIEWSTATE_BEGIN|0663k000002asoA
11:42:28.5 (1614323990)|VF_SERIALIZE_VIEWSTATE_END XXXXXXXXXXXXXXXX
11:48:59.879 (392879638294)|CUMULATIVE_LIMIT_USAGE XXXXXXXXXXXXXXXX
11:48:59.879 (392879638294)|LIMIT_USAGE_FOR_NS|(default)|
Number of SOQL queries: 0 out of 100
Number of query rows: 0 out of 50000
Number of SOSL queries: 0 out of 20
Number of DML statements: 0 out of 150
Number of DML rows: 0 out of 10000
Maximum CPU time: 461 out of 10000
Maximum heap size: 0 out of 6000000
Number of callouts: 0 out of 100
Number of Email Invocations: 0 out of 10
Number of future calls: 0 out of 50
Number of queueable jobs added to the queue: 0 out of 50
Number of Mobile Apex push calls: 0 out of 10
11:48:59.879 (392879638294)|LIMIT_USAGE_FOR_NS|cve|
Number of SOQL queries: 1 out of 100
Number of query rows: 1 out of 50000
Number of SOSL queries: 0 out of 20
Number of DML statements: 0 out of 150
Number of DML rows: 0 out of 10000
Maximum CPU time: 0 out of 10000
Maximum heap size: 0 out of 6000000
Number of callouts: 0 out of 100
Number of Email Invocations: 0 out of 10
Number of future calls: 0 out of 50
Number of queueable jobs added to the queue: 0 out of 50
Number of Mobile Apex push calls: 0 out of 10
11:48:59.879 (392879638294)|CUMULATIVE_LIMIT_USAGE_END
11:48:59.879 (392879825168)|CODE_UNIT_FINISHED|VF: /apex/cve__claimintakewizardbenefitstep
11:48:59.879 (392881965050)|EXECUTION_FINISHED
i.e. a 6 minute+ delay after VF_SERIALIZE_VIEWSTATE_END (marked with XXX above). As can be seen from the limit usage there is no DML, so database locking seems unlikely. All other <apex:commandButton .../> cases are working fine so far.
Are others experiencing this sort of problem? I couldn't find anything via Google.
PS
I've just created a Salesforce support case on this #25293687.
PPS
Slow progress with support, but just having retested in one of the problem orgs, the problem is no longer happening. We have changed nothing, so perhaps Salesforce have. When my colleagues have checked a couple more orgs, I'll close this (and the support case) down.
StaticResourcerow query with plenty of Apex code having executed afterward. I just added a PPS to the question to say it looks like the problem has gone away so this is likely to remain a mystery. – Keith C Jan 08 '20 at 18:16