Long updates by primary key

Update on public.transactions  (cost=0.57..8.59 rows=1 width=2373) (actual rows=0 loops=1)	  Buffers: shared hit=629177 read=399611 dirtied=353681 written=4702	  I/O Timings: read=4189592.228 write=242.336	  ->  Index Scan using transactions_pkey on public.transactions  (cost=0.57..8.59 rows=1 width=2373) (actual rows=1 loops=1)	        Output: id, companyid, idinouterservice, date, status, category, contragentname, contragentinn, contragentbankaccountnumber, contragentbankname, contragentbankbic, currency, amount, bankaccountid, bankaccountnumber, paymentpurpose, contragentkpp, amountall, executestamp, registerstamp, docmodule, doctype, docnumber, accid, bankbik, corraccid, agreerules, sendtype, opertype, urgenttype, ndstypeid, corrtype, uin, kbk, okato, ground, tax1, tax2, tax3, taxdocnum, taxdocdate, taxtype, stat, contragentshortname, infavorites, outerservicestatus, authorid, notify_needed, notify_email, notify_text, paymenttype, nds, contragentid, contragentbankid, ifnscontragentid, dateref, transferbankaccountid, ibsoid, currencytransferamount, groupname, contragentbankswift, currencyoperationcode, contragentcountry, contragentcity, contragentaddress, contragentbankcorrespondentid, contragentbankcorrespondentaccountnumber, contragentbankcorrespondentname, contragentbankcorrespondentswift, mailtobankid, mailtobanksended, payuntil, inquiryid, comissionbankaccountid, comissionaccid, paymentreasondocs, inquirydate, inquirydocnumber, moddate, declineinfo, transferkind, amountnat, absid, dboid, contragentbankcorraccount, corraccisbankclient, corraccisourbank, accibsoid, companyname, companyinn, companykpp, lasteditwithrootfirmware, children, parentid, ishidden, signstatus, contragentcurrency, amountforcredittocurrentaccount, NULL::json, favoritename, importedfrom, payrollid, parentdboid, rrn, approval_code, chargestype, startbankaccountbalance, timeref, formnumber, additionalinfo, corramount, createstamp, signercert, dboadditionalinfo, signdate, communalpaymentinfo, taxtransactionid, mergefield, bankproductid, contragentclientid, addinfavoritesdate, favoritefromid, terminalname, cardpan, pcdate, bankname, banknameplace, contragentbanknameplace, bankcorraccount, comissionbankaccountnumber, taxthirdpersonname, creditlineamount, currfundtransfernotificationid, displaycontragentname, notify_phone, contragentbankaccountnumberforprint, comissionchildren, comissionparentid, smallcurrdealreason, delayeddue, regularpaymentid, skipcurrencycontrol, dbupdatetime, ctid	        Index Cond: (transactions.id = 'd926d582-8a94-4674-a400-ad2f02571c0e'::uuid)	        Buffers: shared hit=5 read=1	        I/O Timings: read=0.018

This query has been executed for 1h10m8s. Index scan node shows actual rows = 1 but then we have actual rows=0 with big counts in Buffers sections. Field id is the primary key of table transactions. Any idea why the update of one row is so long?