According documentation (https://www.ibm.com/support/knowledgecenter/SSGU8G_12.1.0/com.ibm.sqls.doc/ids_sqs_0734.htm) the drop sequence statement looks like:
>>-DROP SEQUENCE--+-----------+--+-------------+--sequence----->< '-IF EXISTS-' '- owner -- . '
It doesn't support restrict keyword. Hibernate's InformixDialect contains this word.
@Override public String getDropSequenceString(String sequenceName) { return "drop sequence " + sequenceName + " restrict"; }
It should be just removed from dealect.